Solve (2x-1/2)(x-2¼): Find When Function is Positive

Quadratic Inequalities with Mixed Number Roots

Look at the function below:

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

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Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Look at the function below:

y=(2x12)(x214) y=\left(2x-\frac{1}{2}\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 will examine the intervals defined by the roots of the quadratic function.

Step 1: Find the roots of each factor:
For 2x12=0 2x - \frac{1}{2} = 0 , solve for x x :
2x=12x=14 2x = \frac{1}{2} \quad \Rightarrow \quad x = \frac{1}{4}
For x214=0 x - 2\frac{1}{4} = 0 , solve for x x :
x=214 x = 2\frac{1}{4}

Step 2: Determine the test intervals around these roots, which are x<14 x < \frac{1}{4} , 14<x<214 \frac{1}{4} < x < 2\frac{1}{4} , and x>214 x > 2\frac{1}{4} .

Step 3: Test each interval to determine where the product is positive:

  • For x<14 x < \frac{1}{4} , both factors (2x12) (2x - \frac{1}{2}) and (x214) (x - 2\frac{1}{4}) are negative, so the product is positive.
  • For 14<x<214 \frac{1}{4} < x < 2\frac{1}{4} , one factor is positive (2x12)(2x - \frac{1}{2}) and the other is negative (x214)(x - 2\frac{1}{4}), resulting in a negative product.
  • For x>214 x > 2\frac{1}{4} , both factors (2x12) (2x - \frac{1}{2}) and (x214) (x - 2\frac{1}{4}) are positive, so the product is positive.

Therefore, the solution for f(x)>0 f(x) > 0 is when x>214 x > 2\frac{1}{4} or x<14 x < \frac{1}{4} .

The correct choice that matches this analysis is:
x>214 x > 2\frac{1}{4} or x<14 x < \frac{1}{4} .

3

Final Answer

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

Key Points to Remember

Essential concepts to master this topic
  • Rule: Find zeros first, then test intervals between roots
  • Technique: Convert 214 2\frac{1}{4} to 94 \frac{9}{4} before solving
  • Check: Test x = 0: both factors negative, so product positive ✓

Common Mistakes

Avoid these frequent errors
  • Testing sign of individual factors instead of their product
    Don't check if 2x12>0 2x - \frac{1}{2} > 0 separately = wrong intervals! This ignores how multiplication affects signs. Always test the sign of the entire product (2x12)(x214) (2x - \frac{1}{2})(x - 2\frac{1}{4}) in each interval.

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 we find the zeros first?

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The zeros are where the function changes from positive to negative (or vice versa). These critical points divide the number line into intervals where the function keeps the same sign.

How do I remember which intervals are positive?

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Use the sign chart method! Test one point in each interval. For example, test x = 0: (2(0)12)(0214)=(12)(214)>0 (2(0) - \frac{1}{2})(0 - 2\frac{1}{4}) = (-\frac{1}{2})(-2\frac{1}{4}) > 0

What if I get confused with the mixed numbers?

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Convert everything to improper fractions first! 214=94 2\frac{1}{4} = \frac{9}{4} makes calculations much clearer and reduces errors.

Why is the answer 'or' instead of 'and'?

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We want ALL x-values where f(x) > 0. Since the function is positive in two separate regions, we use 'or' to include both: x<14 x < \frac{1}{4} OR x>214 x > 2\frac{1}{4} .

Do I include the zeros in my final answer?

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No! The inequality is f(x) > 0, which means strictly greater than zero. At the zeros, f(x) = 0, so they're not included in the solution.

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