Solve (2x-1/2)(x-2.25): Finding Negative Domain Regions

Quadratic Inequalities with Factored Form

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

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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 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

2

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} .

3

Final Answer

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

Key Points to Remember

Essential concepts to master this topic
  • Zero Rule: Set each factor equal to zero to find roots
  • Interval Testing: Choose test points like x = 1 between roots 14 \frac{1}{4} and 214 2\frac{1}{4}
  • Sign Check: Verify f(1) = -15/8 < 0 confirms negative interval ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting to test intervals between roots
    Don't assume the function is negative everywhere just because you found roots! This gives incomplete or wrong solution intervals. The sign of a quadratic changes at each root, so you must test each interval separately. Always check test points in every interval to determine where f(x) < 0.

Practice Quiz

Test your knowledge with interactive questions

The graph of the function below intersects the X-axis at points A and B.

The vertex of the parabola is marked at point C.

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

AAABBBCCCX

FAQ

Everything you need to know about this question

Why do I need to find the roots first?

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The roots are where the function equals zero, and they divide the number line into intervals. The function can only change from positive to negative (or vice versa) at these points!

How do I choose good test points?

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Pick simple numbers in each interval that are easy to calculate with. For example, use x = 0 for intervals containing zero, or x = 1, x = 2, etc.

What if I get the wrong sign when testing?

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Double-check your arithmetic! Remember that negative times negative equals positive, and positive times negative equals negative. Write out each step carefully.

Why is the answer an interval and not just points?

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We want f(x)<0 f(x) < 0 , which means all values where the function is negative, not just where it equals zero. That's why we get an interval like 14<x<214 \frac{1}{4} < x < 2\frac{1}{4} .

Do I include the roots in my final answer?

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No! The roots make f(x) = 0, but we need f(x) < 0 (strictly less than). So use open intervals with < symbols, not ≤ symbols.

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