Solve (x-1/3)(-x-2¼): Finding Negative Function Values and Domain

Quadratic Inequalities with Mixed Number Roots

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

❤️ Continue Your Math Journey!

We have hundreds of course questions with personalized recommendations + Account 100% premium

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

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

2

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

3

Final Answer

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

Key Points to Remember

Essential concepts to master this topic
  • Roots: Set each factor equal to zero to find critical points
  • Sign Analysis: Test intervals between roots: x=3 x = -3 gives negative result
  • Check: Substitute test values to verify sign changes at each root ✓

Common Mistakes

Avoid these frequent errors
  • Incorrectly determining which intervals make the function negative
    Don't assume the middle interval is always positive = wrong solution region! Students often forget that factor signs change at each root. Always test a point in each interval to determine the actual sign of the product.

Practice Quiz

Test your knowledge with interactive questions

The graph of the function below does not intersect the \( x \)-axis.

The parabola's vertex is marked A.

Find all values of \( x \) where
\( f\left(x\right) > 0 \).

AAAX

FAQ

Everything you need to know about this question

How do I find the roots when I have mixed numbers like 2¼?

+

Convert mixed numbers to improper fractions first! 214=94 2\frac{1}{4} = \frac{9}{4} , so x214=0 -x - 2\frac{1}{4} = 0 becomes x=94 x = -\frac{9}{4} .

Why do I need to test points in each interval?

+

The sign of the product changes at each root! Testing points tells you whether each interval gives positive or negative values for f(x) f(x) .

What happens at the roots themselves?

+

At the roots, f(x)=0 f(x) = 0 , so they're not included in the solution for f(x)<0 f(x) < 0 . Use open intervals like (a,b) (a,b) .

How do I remember which intervals to include?

+

Draw a sign chart! Mark the roots on a number line, test one point in each interval, and shade the regions where your test gives a negative result.

What if I get confused about factor signs?

+

Remember: (xa) (x - a) is negative when x<a x < a and positive when x>a x > a . For (xb) (-x - b) , factor out the negative first!

🌟 Unlock Your Math Potential

Get unlimited access to all 18 The Quadratic Function questions, detailed video solutions, and personalized progress tracking.

📹

Unlimited Video Solutions

Step-by-step explanations for every problem

📊

Progress Analytics

Track your mastery across all topics

🚫

Ad-Free Learning

Focus on math without distractions

No credit card required • Cancel anytime

More Questions

Click on any question to see the complete solution with step-by-step explanations