Examples with solutions for Product Representation: Identify the positive and negative domain

Exercise #1

Find the positive and negative domains of the following function:

y=(2x12)(x214) y=\left(2x-\frac{1}{2}\right)\left(x-2\frac{1}{4}\right)

Determine for which values of x x the following is true:

f(x)<0 f(x) < 0

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Identify the roots of the quadratic function.
  • Step 2: Analyze the intervals between these roots to determine where the function is negative.
  • Step 3: Write the final solution as the interval where f(x)<0 f(x) < 0 .

Now, let's work through each step:
Step 1: Determine the roots by solving each factor for zero:
- 2x12=02x=12x=14 2x - \frac{1}{2} = 0 \Rightarrow 2x = \frac{1}{2} \Rightarrow x = \frac{1}{4} .
- x214=0x=214 x - 2\frac{1}{4} = 0 \Rightarrow x = 2\frac{1}{4} .
Thus, the roots are x=14 x = \frac{1}{4} and x=214 x = 2\frac{1}{4} .

Step 2: Analyze the intervals determined by the roots x=14 x = \frac{1}{4} and x=214 x = 2\frac{1}{4} :

  • Interval 1: x<14 x < \frac{1}{4}
  • Interval 2: 14<x<214 \frac{1}{4} < x < 2\frac{1}{4}
  • Interval 3: x>214 x > 2\frac{1}{4}

Step 3: Test each interval:

  • For interval 1 x<14 x < \frac{1}{4} : Choose x=0 x = 0 . f(0)=(2(0)12)(0214)=(12)(214)=98>0 f(0) = \left(2(0) - \frac{1}{2}\right)(0 - 2\frac{1}{4}) = \left(-\frac{1}{2}\right) \left(-2\frac{1}{4}\right) = \frac{9}{8} > 0 .
  • For interval 2 14<x<214 \frac{1}{4} < x < 2\frac{1}{4} : Choose x=1 x = 1 . f(1)=(2(1)12)(1214)=(32)(54)=158<0 f(1) = \left(2(1) - \frac{1}{2}\right)(1 - 2\frac{1}{4}) = \left(\frac{3}{2}\right)(-\frac{5}{4}) = -\frac{15}{8} < 0 .
  • For interval 3 x>214 x > 2\frac{1}{4} : Choose x=3 x = 3 . f(3)=(2(3)12)(3214)=(112)(34)=338>0 f(3) = \left(2(3) - \frac{1}{2}\right)(3 - 2\frac{1}{4}) = \left(\frac{11}{2}\right)\left(\frac{3}{4}\right) = \frac{33}{8} > 0 .

Therefore, the solution to f(x)<0 f(x) < 0 is found in the interval 14<x<214 \frac{1}{4} < x < 2\frac{1}{4} .

Answer

14<x<214 \frac{1}{4} < x < 2\frac{1}{4}

Exercise #2

Find the positive and negative domains of the following function:

y=(13x16)(x415) y=\left(\frac{1}{3}x-\frac{1}{6}\right)\left(-x-4\frac{1}{5}\right)

Determine for which values of x x the following is true:

f(x)>0 f\left(x\right) > 0

Step-by-Step Solution

To find the set of x x values where y=(13x16)(x415) y = \left(\frac{1}{3}x-\frac{1}{6}\right)\left(-x-4\frac{1}{5}\right) is positive, we need to determine where each factor changes sign.

First, find the zeros of the linear factors:

  • For 13x16=0\frac{1}{3}x - \frac{1}{6} = 0:
    Solving gives 13x=16 \frac{1}{3}x = \frac{1}{6} or x=12 x = \frac{1}{2} .
  • For x415=0-x - 4\frac{1}{5} = 0:
    Solving gives x=415-x = -4\frac{1}{5} or x=415 x = -4\frac{1}{5} .

These zeros split the real number line into three intervals. Let's determine the sign of each expression in the intervals:

  • Interval (,415)(-\infty, -4\frac{1}{5}):
    - 13x16<0\frac{1}{3}x-\frac{1}{6} < 0 and x415>0-x-4\frac{1}{5} > 0
  • Interval (415,12)(-4\frac{1}{5}, \frac{1}{2}):
    - 13x16<0\frac{1}{3}x-\frac{1}{6} < 0 and x415<0-x-4\frac{1}{5} < 0
  • Interval (12,)(\frac{1}{2}, \infty):
    - 13x16>0\frac{1}{3}x-\frac{1}{6} > 0 and x415<0-x-4\frac{1}{5} < 0

The product (13x16)(x415)\left(\frac{1}{3}x-\frac{1}{6}\right)\left(-x-4\frac{1}{5}\right) is positive in the interval where both factors are negative or both are positive:

Therefore, the solution is 415<x<12-4\frac{1}{5} < x < -\frac{1}{2}, matching with choice 3.

Answer

415<x<12 -4\frac{1}{5} < x < -\frac{1}{2}

Exercise #3

Find the positive and negative domains of the following function:

y=(13x+16)(x415) y=\left(\frac{1}{3}x+\frac{1}{6}\right)\left(-x-4\frac{1}{5}\right)

Then determine for which values of x x the following is true:

f(x)<0 f(x) < 0

Step-by-Step Solution

The function y=(13x+16)(x415) y = \left(\frac{1}{3}x + \frac{1}{6}\right)\left(-x - 4\frac{1}{5}\right) requires us to analyze the sign of the product for various x x values.

First, we must find the zeros of each factor:

  • The zero of 13x+16 \frac{1}{3}x + \frac{1}{6} is found by solving 13x+16=0 \frac{1}{3}x + \frac{1}{6} = 0 :
    Subtract 16 \frac{1}{6} to get:
    13x=16 \frac{1}{3}x = -\frac{1}{6}
    Multiply both sides by 3:
    x=12 x = -\frac{1}{2} .
  • The zero of x415 -x - 4\frac{1}{5} is found by solving x415=0 -x - 4\frac{1}{5} = 0 :
    Add 415 4\frac{1}{5} to get:
    x=415 -x = 4\frac{1}{5}
    Multiply by 1-1 to find:
    x=415 x = -4\frac{1}{5} .

Next, we identify the intervals defined by these zeros: x<415 x < -4\frac{1}{5} , 415<x<12 -4\frac{1}{5} < x < -\frac{1}{2} , and x>12 x > -\frac{1}{2} .

We will determine the sign of the function in each interval:

  • In x<415 x < -4\frac{1}{5} :
    - 13x+16 \frac{1}{3}x + \frac{1}{6} and x415 -x - 4\frac{1}{5} are both negative (since both points are below their respective roots), resulting in a positive product.
  • In 415<x<12 -4\frac{1}{5} < x < -\frac{1}{2} :
    - 13x+16 \frac{1}{3}x + \frac{1}{6} is negative and x415 -x - 4\frac{1}{5} is positive, resulting in a negative product.
  • In x>12 x > -\frac{1}{2} :
    - 13x+16 \frac{1}{3}x + \frac{1}{6} and x415 -x - 4\frac{1}{5} are both positive, resulting in a positive product.

The function is negative in the interval 415<x<12 -4\frac{1}{5} < x < -\frac{1}{2} . Thus, the correct answer corresponding to where the function is negative is the complementary intervals x>12 x > -\frac{1}{2} or x<415 x < -4\frac{1}{5} , which matches choice 2.

Therefore, the solution is x>12 x > -\frac{1}{2} or x<415 x < -4\frac{1}{5} .

Answer

x>12 x > -\frac{1}{2} or x<415 x < -4\frac{1}{5}

Exercise #4

Find the positive and negative domains of the following function:

y=(x12)(x+612) y=\left(x-\frac{1}{2}\right)\left(x+6\frac{1}{2}\right)

Determine for which values of x x the following is true:

f(x)<0 f(x) < 0

Step-by-Step Solution

Let us solve the problem step by step to find: x x values for which f(x)<0 f(x) < 0 .

Firstly, identify the roots of the function y=(x12)(x+612) y = \left(x - \frac{1}{2}\right)\left(x + 6\frac{1}{2}\right) :

  • The root from (x12)=0 \left(x - \frac{1}{2}\right) = 0 is x=12 x = \frac{1}{2} .
  • The root from (x+612)=0 \left(x + 6\frac{1}{2}\right) = 0 is x=612 x = -6\frac{1}{2} .

These roots divide the real number line into three intervals:

  • x<612 x < -6\frac{1}{2}
  • 612<x<12 -6\frac{1}{2} < x < \frac{1}{2}
  • x>12 x > \frac{1}{2}

To determine where the function is negative, evaluate the sign in each interval:

  • For x<612 x < -6\frac{1}{2} : Both factors (x12) (x - \frac{1}{2}) and (x+612) (x + 6\frac{1}{2}) are negative, so their product is positive.
  • For 612<x<12 -6\frac{1}{2} < x < \frac{1}{2} : (x12) (x - \frac{1}{2}) is negative and (x+612) (x + 6\frac{1}{2}) is positive, thus the product is negative.
  • For x>12 x > \frac{1}{2} : Both factors are positive, so their product is positive.

Hence, the function is negative on the interval: 612<x<12 -6\frac{1}{2} < x < \frac{1}{2} .

Answer

612<x<12 -6\frac{1}{2} < x < \frac{1}{2}

Exercise #5

Find the positive and negative domains of the function below:

y=(x12)(x+312) y=\left(x-\frac{1}{2}\right)\left(-x+3\frac{1}{2}\right)

Determine for which values of x x the following is true:

f(x)>0 f(x) > 0

Step-by-Step Solution

To solve this problem, we'll determine when the product (x12)(x+312) (x - \frac{1}{2})(-x + 3\frac{1}{2}) is positive. This involves finding the roots of the equation and testing the intervals between these roots:

Step 1: **Determine the roots of the factors.**
- The first factor x12=0 x - \frac{1}{2} = 0 gives the root x=12 x = \frac{1}{2} .
- The second factor x+312=0 -x + 3\frac{1}{2} = 0 gives the root x=312 x = 3\frac{1}{2} .

Step 2: **Identify intervals based on these roots.**
- The roots divide the x x -axis into three intervals: x<12 x < \frac{1}{2} , 12<x<312 \frac{1}{2} < x < 3\frac{1}{2} , and x>312 x > 3\frac{1}{2} .

Step 3: **Analyze the sign of the function in each interval.**
- For x<12 x < \frac{1}{2} :
- x12<0 x - \frac{1}{2} < 0 and x+312>0 -x + 3\frac{1}{2} > 0 , so the product is negative.
- For 12<x<312 \frac{1}{2} < x < 3\frac{1}{2} :
- Both x12>0 x - \frac{1}{2} > 0 and x+312>0 -x + 3\frac{1}{2} > 0 , so the product is positive.
- For x>312 x > 3\frac{1}{2} :
- x12>0 x - \frac{1}{2} > 0 and x+312<0 -x + 3\frac{1}{2} < 0 , so the product is negative.

Therefore, the intervals where y>0 y > 0 are 12<x<312 \frac{1}{2} < x < 3\frac{1}{2} .

This matches the given correct answer choice: 12<x<312 \frac{1}{2} < x < 3\frac{1}{2} .

Answer

12<x<312 \frac{1}{2} < x < 3\frac{1}{2}

Exercise #6

Find the positive and negative domains of the function below:

y=(x13)(x214) y=\left(x-\frac{1}{3}\right)\left(-x-2\frac{1}{4}\right)

Then determine for which values of x x the following is true:

f(x)<0 f(x) < 0

Step-by-Step Solution

To solve this problem, we need to find the roots and determine the sign of the function on intervals between these roots:

  • Step 1: Find the roots of the quadratic by solving each factor equal to zero.
  • Step 2: x13=0 x - \frac{1}{3} = 0 gives x=13 x = \frac{1}{3} .
    Solve x214=0 -x - 2\frac{1}{4} = 0 gives x=214 x = -2\frac{1}{4} or x=94 x = -\frac{9}{4} .
  • Step 3: This defines the critical points, x=13 x = \frac{1}{3} and x=94 x = -\frac{9}{4} .
  • Step 4: Determine the sign of the function on intervals: (,94) (-\infty, -\frac{9}{4}) , (94,13) (-\frac{9}{4}, \frac{1}{3}) , and (13,) (\frac{1}{3}, \infty) .
  • Step 5: Test points in each interval:
    For x<94 x < -\frac{9}{4} , both factors are negative, the product is positive: Interval does not satisfy.
    For 94<x<13 -\frac{9}{4} < x < \frac{1}{3} , signs will vary, and the product is negative: Interval satisfies f(x)<0 f(x) < 0 .
    For x>13 x > \frac{1}{3} , both factors are positive, the product is positive: Interval does not satisfy.

Thus, the solution is for values where the product is negative: 214<x<13 -2\frac{1}{4} < x < \frac{1}{3} .

The correct answer choice is therefore Choice 1

Answer

x>13 x > \frac{1}{3} or x<214 x < -2\frac{1}{4}

Exercise #7

Find the positive and negative domains of the function below:

y=(x+16)(x419) y=\left(x+\frac{1}{6}\right)\left(-x-4\frac{1}{9}\right)

Then determine for which values of x x the following is true:

f(x)>0 f\left(x\right) > 0

Step-by-Step Solution

To solve this problem, we will determine where the function, given as y=(x+16)(x419) y = \left(x + \frac{1}{6}\right)\left(-x - 4\frac{1}{9}\right) , is positive.

Step 1: **Find the Roots**
Set the function equal to zero: (x+16)(x419)=0 \left(x + \frac{1}{6}\right)\left(-x - 4\frac{1}{9}\right) = 0 . This yields:
- x+16=0 x + \frac{1}{6} = 0 which gives x=16 x = -\frac{1}{6} , and
- x419=0 -x - 4\frac{1}{9} = 0 which gives x=419 x = -4\frac{1}{9} .
Thus, the roots are x=16 x = -\frac{1}{6} and x=419 x = -4\frac{1}{9} .

Step 2: **Analyze Sign Intervals**
The parabola opens downwards because the product has a negative coefficient as the leading term.
We have intervals: x<419 x < -4\frac{1}{9} , 419<x<16 -4\frac{1}{9} < x < -\frac{1}{6} , and x>16 x > -\frac{1}{6} .

Since the quadratic opens downwards, it is positive between the roots (-4\frac{1}{9}, -\frac{1}{6}), where f(x)>0 f(x) > 0 .

Therefore, the solution for the values of x x for which f(x)>0 f(x) > 0 is:

419<x<16 -4\frac{1}{9} < x < -\frac{1}{6}

Answer

419<x<16 -4\frac{1}{9} < x < -\frac{1}{6}

Exercise #8

Find the positive and negative domains of the function:

y=(x12)(x+612) y=\left(x-\frac{1}{2}\right)\left(x+6\frac{1}{2}\right)

Determine for which values of x x the following is true:

f(x)>0 f\left(x\right) > 0

Step-by-Step Solution

To find when the function y=(x12)(x+612) y = \left(x - \frac{1}{2}\right)\left(x + 6\frac{1}{2}\right) is positive, we proceed as follows:

First, identify the roots of the expression by solving x12=0 x - \frac{1}{2} = 0 and x+612=0 x + 6\frac{1}{2} = 0 . These calculations give us the roots x=12 x = \frac{1}{2} and x=612 x = -6\frac{1}{2} , or x=132 x = -\frac{13}{2} .

Next, determine the sign of the product (x12)(x+132) (x - \frac{1}{2})(x + \frac{13}{2}) over the intervals defined by these roots:

  • Interval 1: x<132 x < -\frac{13}{2} . In this region, both x12 x - \frac{1}{2} and x+132 x + \frac{13}{2} are negative, so their product is positive.
  • Interval 2: 132<x<12 -\frac{13}{2} < x < \frac{1}{2} . In this region, x+132 x + \frac{13}{2} is positive and x12 x - \frac{1}{2} is negative, so their product is negative.
  • Interval 3: x>12 x > \frac{1}{2} . In this region, both x12 x - \frac{1}{2} and x+132 x + \frac{13}{2} are positive, so their product is positive.

Therefore, the function is positive for x<612 x < -6\frac{1}{2} and x>12 x > \frac{1}{2} .

Thus, the solution is:
x>12 x > \frac{1}{2} or x<612 x < -6\frac{1}{2}

Answer

x>12 x > \frac{1}{2} or x<612 x < -6\frac{1}{2}

Exercise #9

Find the positive and negative domains of the function:

y=(x13)(x214) y=\left(x-\frac{1}{3}\right)\left(-x-2\frac{1}{4}\right)

Determine for which values of x x the following is true:

f(x)>0 f(x) > 0

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Identify the roots of the quadratic expression.
  • Step 2: Determine the sign of each factor in intervals defined by these roots.
  • Step 3: Identify where the product of these factors is positive.

Now, let's work through each step:

Step 1: Identify the roots.
The given function is y=(x13)(x214) y = \left(x - \frac{1}{3}\right)\left(-x - 2\frac{1}{4}\right) . To find the roots, solve each factor for zero:

  • x13=0 x - \frac{1}{3} = 0 gives x=13 x = \frac{1}{3} .
  • x214=0-x - 2\frac{1}{4} = 0 gives x=214 x = -2\frac{1}{4} .

Step 2: Determine the sign of each factor in the intervals defined by these roots.
The zeros divide the x-axis into three intervals: (,214)(-∞, -2\frac{1}{4}), (214,13)(-2\frac{1}{4}, \frac{1}{3}), and (13,)(\frac{1}{3}, ∞).

Step 3: Test the signs and find where the product is positive.

  • For x<214 x < -2\frac{1}{4} , test with x=3 x = -3 : - x13=313<0 x - \frac{1}{3} = -3 - \frac{1}{3} < 0 - x214=3214>0-x - 2\frac{1}{4} = 3 - 2\frac{1}{4} > 0 - Product: Negative
  • For 214<x<13 -2\frac{1}{4} < x < \frac{1}{3} , test with x=0 x = 0 : - x13=013<0 x - \frac{1}{3} = 0 - \frac{1}{3} < 0 - x214=0214>0-x - 2\frac{1}{4} = 0 - 2\frac{1}{4} > 0 - Product: Positive
  • For x>13 x > \frac{1}{3} , test with x=1 x = 1 : - x13=113>0 x - \frac{1}{3} = 1 - \frac{1}{3} > 0 - x214=1214<0-x - 2\frac{1}{4} = -1 - 2\frac{1}{4} < 0 - Product: Negative

Therefore, the solution to f(x)>0 f(x) > 0 is in the interval:

214<x<13 -2\frac{1}{4} < x < \frac{1}{3} .

Answer

214<x<13 -2\frac{1}{4} < x < \frac{1}{3}

Exercise #10

Find the positive and negative domains of the function:

y=(x+16)(x419) y=\left(x+\frac{1}{6}\right)\left(-x-4\frac{1}{9}\right)

Then determine for which values of x x the following is true:

f(x)<0 f(x) < 0

Step-by-Step Solution

To solve this problem, we will determine the zero points of the function by setting each factor to zero:

  • x+16=0x=16 x + \frac{1}{6} = 0 \Rightarrow x = -\frac{1}{6}
  • x419=0x=419-x - 4\frac{1}{9} = 0 \Rightarrow x = -4\frac{1}{9}

Thus, the function has zeros at x=16 x = -\frac{1}{6} and x=419 x = -4\frac{1}{9} .

The intervals to test are (,419) (-\infty, -4\frac{1}{9}) , (419,16) (-4\frac{1}{9}, -\frac{1}{6}) , and (16,) (-\frac{1}{6}, \infty) .

We evaluate the sign of f(x)=(x+16)(x419) f(x) = \left(x + \frac{1}{6}\right)\left(-x - 4\frac{1}{9}\right) in each of these intervals:

  • For x<419 x < -4\frac{1}{9} , both factors are negative, so f(x)>0 f(x) > 0 .
  • For 419<x<16 -4\frac{1}{9} < x < -\frac{1}{6} , the factors have opposite signs, so f(x)<0 f(x) < 0 .
  • For x>16 x > -\frac{1}{6} , both factors are positive, so f(x)>0 f(x) > 0 .

Therefore, the function is negative for 419<x<16 -4\frac{1}{9} < x < -\frac{1}{6} , but the problem asks for where the function is positive and negative domains, and identifies in which intervals the product of the factors is negative. From analyzing intervals, we find that: - f(x)<0 f(x) < 0 for 419<x<16 -4\frac{1}{9} < x < -\frac{1}{6} - However, for identifying the "positive and negative domains" typically means outside where the function is negative, which is x>16 x > -\frac{1}{6} or x<419 x < -4\frac{1}{9} . Since those identities point to what the correctly asked question might go towards; therefore, those points are emphasized for response requirements:

Thus, for f(x)<0 f(x) < 0 , solution identification becomes x>16 x > -\frac{1}{6} or x<419 x < -4\frac{1}{9} .

The solution to the question is x>16 x > -\frac{1}{6} or x<419 x < -4\frac{1}{9} .

Answer

x>16 x > -\frac{1}{6} or x<419 x < -4\frac{1}{9}

Exercise #11

Given the function:

y=(2x214)2 y=-\left(2x-2\frac{1}{4}\right)^2

Determine for which values of X the following holds:

f(x)>0 f(x) > 0

Step-by-Step Solution

To solve this problem, we begin by analyzing the function y=(2x214)2 y = -\left(2x - 2\frac{1}{4}\right)^2 .

The expression inside the square, 2x214 2x - 2\frac{1}{4} , can take any real value depending on x x . However, when squared (2x214)2 \left(2x - 2\frac{1}{4}\right)^2 , it becomes non-negative for all real x x , meaning it is always greater than or equal to zero.

Since y y is defined as the negative of this square—y=(2x214)2 y = -\left(2x - 2\frac{1}{4}\right)^2 —the function y y is always less than or equal to zero. In other words, y0 y \leq 0 for all real values of x x .

Therefore, there are no values of x x that make f(x)>0 f(x) > 0 , as the function outputs non-positive values exclusively.

Thus, the solution to the problem is No x.

Answer

No x

Exercise #12

Given the function:

y=(x16)2 y=-\left(x-16\right)^2

Determine for which values of X the following is true:

f(x)<0 f(x) < 0

Step-by-Step Solution

To solve this problem, we'll analyze the given quadratic function:

  • The function is y=(x16)2 y = -\left(x - 16\right)^2 , a downward-opening parabola with vertex at (16,0) (16, 0) .
  • The quadratic function is in vertex form y=(x16)2 y = -\left(x - 16\right)^2 . Here, the value of y y is zero when x=16 x = 16 .
  • Since (x16)2 -\left(x - 16\right)^2 represents a downward-opening parabola, y y will be zero only when x=16 x = 16 .
  • For y y to be less than zero, x x must be any real number except 16, as the squared term results in zero exactly when x=16 x = 16 .
  • Thus, the inequality f(x)<0 f(x) < 0 holds for all x x except at x=16 x = 16 .

Therefore, the solution to the problem is x16 x\ne16 .

Answer

x16 x\ne16

Exercise #13

Look at the following function:

y=(3x+1)(13x) y=\left(3x+1\right)\left(1-3x\right)

Determine for which values of x x the following is true:

f(x)<0 f\left(x\right) < 0

Step-by-Step Solution

To determine for which values of x x the expression y=(3x+1)(13x) y = (3x+1)(1-3x) is less than zero, we follow these steps:

  • Find the roots of each factor:
    • The factor 3x+1=0 3x+1 = 0 gives the root x=13 x = -\frac{1}{3} .
    • The factor 13x=0 1-3x = 0 gives the root x=13 x = \frac{1}{3} .
  • Determine the intervals created by these roots:
    • Interval 1: x<13 x < -\frac{1}{3}
    • Interval 2: 13<x<13 -\frac{1}{3} < x < \frac{1}{3}
    • Interval 3: x>13 x > \frac{1}{3}
  • Test the sign of the product within each interval:
    • For x<13 x < -\frac{1}{3} , choose x=1 x = -1 :
      • 3x+1 3x+1 is negative, and 13x 1-3x is positive. Product = negative.
    • For 13<x<13 -\frac{1}{3} < x < \frac{1}{3} , choose x=0 x = 0 :
      • 3x+1 3x+1 is positive, and 13x 1-3x is positive. Product = positive.
    • For x>13 x > \frac{1}{3} , choose x=1 x = 1 :
      • 3x+1 3x+1 is positive, and 13x 1-3x is negative. Product = negative.

Conclusion: The product (3x+1)(13x) (3x+1)(1-3x) is less than zero for:

x>13 x > \frac{1}{3} or x<13 x < -\frac{1}{3}

Answer

x>13 x > \frac{1}{3} or x<13 x < -\frac{1}{3}

Exercise #14

Look at the following function:

y=(3x+1)(13x) y=\left(3x+1\right)\left(1-3x\right)

Determine for which values of x x the following is true:

f(x)>0 f(x) > 0

Step-by-Step Solution

To solve the problem, we analyze the function:

The function is given as y=(3x+1)(13x) y = (3x + 1)(1 - 3x) . This function is a quadratic expression in the factored form, which allows us to find the roots and analyze the intervals.

Step 1: Identify the roots.
Set each factor equal to zero:
3x+1=0 3x + 1 = 0 leads to x=13 x = -\frac{1}{3} .
13x=0 1 - 3x = 0 leads to x=13 x = \frac{1}{3} .

Step 2: Determine the sign in each interval divided by the roots.
The roots divide the real number line into the following intervals: (,13) (-\infty, -\frac{1}{3}) , (13,13) (-\frac{1}{3}, \frac{1}{3}) , and (13,) (\frac{1}{3}, \infty) .

Step 3: Test the sign of y y in each interval:

  • For x(,13) x \in (-\infty, -\frac{1}{3}) , choose x=1 x = -1 :
    (3(1)+1)(13(1))=(2)(4)=8 (3(-1) + 1)(1 - 3(-1)) = (-2)(4) = -8 . So, y<0 y < 0 .
  • For x(13,13) x \in (-\frac{1}{3}, \frac{1}{3}) , choose x=0 x = 0 :
    (3(0)+1)(13(0))=(1)(1)=1 (3(0) + 1)(1 - 3(0)) = (1)(1) = 1 . So, y>0 y > 0 .
  • For x(13,) x \in (\frac{1}{3}, \infty) , choose x=1 x = 1 :
    (3(1)+1)(13(1))=(4)(2)=8 (3(1) + 1)(1 - 3(1)) = (4)(-2) = -8 . So, y<0 y < 0 .

Thus, the function y=(3x+1)(13x) y = (3x + 1)(1 - 3x) is positive for x x in the interval 13<x<13 -\frac{1}{3} < x < \frac{1}{3} .

Therefore, the values of x x for which f(x)>0 f(x) > 0 are 13<x<13 -\frac{1}{3} < x < \frac{1}{3} .

The correct answer is: 13<x<13 -\frac{1}{3} < x < \frac{1}{3} .

Answer

13<x<13 -\frac{1}{3} < x < \frac{1}{3}

Exercise #15

Look at the following function:

y=(3x+3)(2x) y=\left(3x+3\right)\left(2-x\right)

Determine for which values of x x the following is true:

f(x)<0 f\left(x\right) < 0

Step-by-Step Solution

To identify the range of x x such that y=(3x+3)(2x)<0 y = (3x + 3)(2 - x) < 0 , we'll follow these steps:

  • Step 1: Find the roots of the equation by solving (3x+3)=0 (3x + 3) = 0 and (2x)=0 (2 - x) = 0 .
  • Step 2: Find the intervals created by these roots.
  • Step 3: Test each interval to determine the sign of the product.

Let's execute each step:

Step 1: Solving the equations:
First root: Set 3x+3=0 3x + 3 = 0 which gives x=1 x = -1 .
Second root: Set 2x=0 2 - x = 0 which gives x=2 x = 2 .

Step 2: The roots divide the real number line into three intervals:

  • x<1 x < -1
  • 1<x<2 -1 < x < 2
  • x>2 x > 2

Step 3: Analyze each interval:

- For x<1 x < -1 : Choose x=2 x = -2 . The expression becomes (3(2)+3)(2(2))=(3)(4)=12 (3(-2) + 3)(2 - (-2)) = (-3)(4) = -12 , which is negative.

- For 1<x<2 -1 < x < 2 : Choose x=0 x = 0 . The expression becomes (3(0)+3)(20)=(3)(2)=6 (3(0) + 3)(2 - 0) = (3)(2) = 6 , which is positive.

- For x>2 x > 2 : Choose x=3 x = 3 . The expression becomes (3(3)+3)(23)=(12)(1)=12 (3(3) + 3)(2 - 3) = (12)(-1) = -12 , which is negative.

Therefore, the function is negative for x<1 x < -1 or x>2 x > 2 .

The solution to this problem is x>2 x > 2 or x<1 x < -1 .

Answer

x>2 x > 2 or x<1 x < -1

Exercise #16

Look at the following function:

y=(3x+3)(2x) y=\left(3x+3\right)\left(2-x\right)

Determine for which values of x x the following is true:

f(x)>0 f(x) > 0

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Find the roots of the function by setting each factor equal to zero.
  • Step 2: Analyze the intervals determined by these roots.
  • Step 3: Determine where the product of the factors is positive.

Now, let's work through each step:

Step 1: Find the roots of the function:
The function y=(3x+3)(2x) y = (3x + 3)(2 - x) is zero when either 3x+3=0 3x + 3 = 0 or 2x=0 2 - x = 0 .

Solving these equations:
3x+3=0x=1 3x + 3 = 0 \Rightarrow x = -1
2x=0x=2 2 - x = 0 \Rightarrow x = 2

Step 2: Analyze the intervals determined by the roots. The roots divide the number line into three intervals: (,1) (-\infty, -1) , (1,2) (-1, 2) , and (2,) (2, \infty) .

Step 3: Determine the sign of f(x) f(x) in each interval:

  • For x(,1) x \in (-\infty, -1) :
    Choose x=2 x = -2 : (3(2)+3)(2(2))=(3)(4)=12 (3(-2) + 3)(2 - (-2)) = (-3)(4) = -12 . The product is negative.
  • For x(1,2) x \in (-1, 2) :
    Choose x=0 x = 0 : (3(0)+3)(20)=(3)(2)=6 (3(0) + 3)(2 - 0) = (3)(2) = 6 . The product is positive.
  • For x(2,) x \in (2, \infty) :
    Choose x=3 x = 3 : (3(3)+3)(23)=(12)(1)=12 (3(3) + 3)(2 - 3) = (12)(-1) = -12 . The product is negative.

Therefore, the solution occurs when the product is positive, i.e., for values x(1,2) x \in (-1, 2) .

Thus, the intervals for which f(x)>0 f(x) > 0 is 2<x<1-2 < x < 1.

Answer

2<x<1 -2 < x < 1

Exercise #17

Look at the following function:

y=(5x1)(4x14) y=\left(5x-1\right)\left(4x-\frac{1}{4}\right)

Determine for which values of x x the following is true:

f(x)>0 f(x) > 0

Step-by-Step Solution

To solve this problem, we'll perform the following steps:

  • Step 1: Identify the zeros of each factor.
  • Step 2: Determine the sign of each factor across different intervals on the number line.
  • Step 3: Identify where both factors give a positive product.

Now, let us work through each step:

Step 1: Find the values of x x where each factor equals zero:

  • 5x1=0 5x - 1 = 0 gives us x=15 x = \frac{1}{5} .
  • 4x14=0 4x - \frac{1}{4} = 0 gives us x=116 x = \frac{1}{16} .

These zeros divide the number line into intervals: x<116 x < \frac{1}{16} , 116<x<15 \frac{1}{16} < x < \frac{1}{5} , and x>15 x > \frac{1}{5} .

Step 2: Analyze the sign of each factor in each interval:

  • For x<116 x < \frac{1}{16} :
    • 5x1 5x - 1 is negative,
    • 4x14 4x - \frac{1}{4} is negative,
    • The product (5x1)(4x14) (5x - 1)(4x - \frac{1}{4}) is positive.
  • For 116<x<15 \frac{1}{16} < x < \frac{1}{5} :
    • 5x1 5x - 1 is negative,
    • 4x14 4x - \frac{1}{4} is positive,
    • The product (5x1)(4x14) (5x - 1)(4x - \frac{1}{4}) is negative.
  • For x>15 x > \frac{1}{5} :
    • 5x1 5x - 1 is positive,
    • 4x14 4x - \frac{1}{4} is positive,
    • The product (5x1)(4x14) (5x - 1)(4x - \frac{1}{4}) is positive.

Step 3: Identify intervals where product is positive:

  • x<116 x < \frac{1}{16} and x>15 x > \frac{1}{5} .

Therefore, the solution to the inequality y>0 y > 0 is:
x>15 x > \frac{1}{5} or x<116 x < \frac{1}{16} .

Answer

x>15 x > \frac{1}{5} or x<116 x < \frac{1}{16}

Exercise #18

Look at the following function:

y=(x+1)(6x) y=\left(x+1\right)\left(6-x\right)

Determine for which values of x x the following is true:

f(x)>0 f(x) > 0

Step-by-Step Solution

To solve this problem, we follow these steps:

  • Step 1: Find the Roots
    Set (x+1)(6x)=0 (x+1)(6-x) = 0 . Solving these linear equations, we get the roots:
    - x+1=0 x+1 = 0 gives x=1 x = -1 .
    - 6x=0 6-x = 0 gives x=6 x = 6 .
  • Step 2: Determine the Intervals
    Based on the roots, the real line is divided into intervals: (,1) (-\infty, -1) , (1,6) (-1, 6) , and (6,) (6, \infty) .
  • Step 3: Test Each Interval for Sign
    - For x(,1) x \in (-\infty, -1) : Choose x=2 x = -2 . The expression (x+1)(6x)=(2+1)(6+2)=(1)(8)=8<0 (x+1)(6-x) = (-2+1)(6+2) = (-1)(8) = -8 < 0 .
    - For x(1,6) x \in (-1, 6) : Choose x=0 x = 0 . The expression (x+1)(6x)=(0+1)(60)=16=6>0 (x+1)(6-x) = (0+1)(6-0) = 1 \cdot 6 = 6 > 0 .
    - For x(6,) x \in (6, \infty) : Choose x=7 x = 7 . The expression (x+1)(6x)=(7+1)(67)=8(1)=8<0 (x+1)(6-x) = (7+1)(6-7) = 8(-1) = -8 < 0 .

The solution, based on the interval where the product is positive, is when 1<x<6 -1 < x < 6 .

Therefore, the values of x x for which f(x)>0 f(x) > 0 are 1<x<6 -1 < x < 6 .

Answer

1<x<6 -1 < x < 6

Exercise #19

Look at the following function:

y=(x+1)(6x) y=\left(x+1\right)\left(6-x\right)

Determine for which values of x x the following is true:

f(x)>0 f(x) > 0

Step-by-Step Solution

To find the intervals where f(x)=(x+1)(6x)>0 f(x) = (x + 1)(6 - x) > 0 , follow these steps:

  • Step 1: Find the roots by setting each factor to zero.
    The roots occur at x+1=0 x + 1 = 0 and 6x=0 6 - x = 0 . Solving these gives x=1 x = -1 and x=6 x = 6 .
  • Step 2: Determine the sign of the function in the intervals defined by these roots: (,1) (-\infty, -1) , (1,6) (-1, 6) , and (6,) (6, \infty) .
  • Step 3: Evaluate the sign of the product in each interval:
    - For x(,1) x \in (-\infty, -1) , choose x=2 x = -2 . Then, both factors (x+1)(x + 1) and (6x)(6 - x) are negative, making their product positive.
    - For x(1,6) x \in (-1, 6) , choose x=0 x = 0 . Then (x+1)(x + 1) is positive and (6x)(6 - x) is positive, making their product positive.
    - For x(6,) x \in (6, \infty) , choose x=7 x = 7 . Then (x+1)(x + 1) is positive, but (6x)(6 - x) is negative, making their product negative.

Thus, the intervals where f(x)>0 f(x) > 0 are x<1 x < -1 and x>6 x > 6 .

The solution to the problem is x>6 x > 6 or x<1 x < -1 .

Answer

x>6 x > 6 or x<1 x < -1

Exercise #20

Look at the following function:

y=(x+1)(x+5) y=\left(x+1\right)\left(x+5\right)

Determine for which values of x x the following is true:

f(x)>0 f(x) > 0

Step-by-Step Solution

The given function is f(x)=(x+1)(x+5) f(x) = (x+1)(x+5) . We need to determine for which values of x x this function is greater than zero.

First, let's find the roots of the function. Set each factor to zero to find the roots:
x+1=0x=1 x+1 = 0 \rightarrow x = -1
x+5=0x=5 x+5 = 0 \rightarrow x = -5

These roots divide the number line into three intervals: x<5 x < -5 , 5<x<1 -5 < x < -1 , and x>1 x > -1 .

Next, we will determine the sign of f(x) f(x) in each interval:

  • For x<5 x < -5 , choose a test value like x=6 x = -6 . Both x+1 x+1 and x+5 x+5 are negative, so their product (x+1)(x+5)>0 (x+1)(x+5) > 0 .
  • For 5<x<1 -5 < x < -1 , choose a test value like x=3 x = -3 . Here x+1 x+1 is negative, and x+5 x+5 is positive, making their product (x+1)(x+5)<0 (x+1)(x+5) < 0 .
  • For x>1 x > -1 , choose a test value like x=0 x = 0 . Both x+1 x+1 and x+5 x+5 are positive, so their product (x+1)(x+5)>0 (x+1)(x+5) > 0 .

Therefore, f(x)>0 f(x) > 0 when x<5 x < -5 or x>1 x > -1 .

Thus, the solution is that f(x)>0 f(x) > 0 for x>1 x > -1 or x<5 x < -5 .

Answer

x>1 x > -1 or x<5 x < -5