Solve the Quadratic: Where 1/4x² - 3.5x Is Positive

Look at the following function:

y=14x2312x y=\frac{1}{4}x^2-3\frac{1}{2}x

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

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1

Understand the problem

Look at the following function:

y=14x2312x y=\frac{1}{4}x^2-3\frac{1}{2}x

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

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

2

Step-by-step solution

To solve the problem of finding for which values of x x the function y=14x272x y = \frac{1}{4}x^2 - \frac{7}{2}x is greater than zero, follow these steps:

  • Step 1: Identify the function. The quadratic function y=14x272x y = \frac{1}{4}x^2 - \frac{7}{2}x can be rewritten as y=14x272x y = \frac{1}{4}x^2 - \frac{7}{2}x .
  • Step 2: Use the quadratic formula to find the roots of the equation y=0 y = 0 . The quadratic formula is:
x=b±b24ac2a x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

Here, a=14 a = \frac{1}{4} , b=72 b = -\frac{7}{2} , and c=0 c = 0 .

  • Step 3: Calculate b24ac b^2 - 4ac :
b24ac=(72)24(14)(0)=494 b^2 - 4ac = \left(-\frac{7}{2}\right)^2 - 4 \left(\frac{1}{4}\right)(0) = \frac{49}{4}
  • Step 4: Find the roots using the quadratic formula:
x=(72)±4942×14 x = \frac{-\left(-\frac{7}{2}\right) \pm \sqrt{\frac{49}{4}}}{2 \times \frac{1}{4}} x=72±7212 x = \frac{\frac{7}{2} \pm \frac{7}{2}}{\frac{1}{2}} x=7±71 x = \frac{7 \pm 7}{1}

This gives two roots: x=0 x = 0 and x=14 x = 14 .

  • Step 5: Determine the intervals defined by these roots. We have three intervals to check: x<0 x < 0 , 0<x<14 0 < x < 14 , and x>14 x > 14 .
  • Step 6: Test the sign of f(x) f(x) in each interval:
  • For x<0 x < 0 , choose x=1 x = -1 :
f(1)=14(1)272(1)=14+72>0 f(-1) = \frac{1}{4}(-1)^2 - \frac{7}{2}(-1) = \frac{1}{4} + \frac{7}{2} > 0
  • For 0<x<14 0 < x < 14 , choose x=1 x = 1 :
f(1)=14(1)272(1)=1472<0 f(1) = \frac{1}{4}(1)^2 - \frac{7}{2}(1) = \frac{1}{4} - \frac{7}{2} < 0
  • For x>14 x > 14 , choose x=15 x = 15 :
f(15)=14(15)272(15)=22541052>0 f(15) = \frac{1}{4}(15)^2 - \frac{7}{2}(15) = \frac{225}{4} - \frac{105}{2} > 0

After confirming the signs, we find that f(x)>0 f(x) > 0 for x<0 x \lt 0 and x>14 x \gt 14 .

Therefore, the solution to the problem is <strong>x>14 <strong>x > 14 or x<0 x < 0.

3

Final Answer

x>14 x > 14 or x<0 x < 0

Practice Quiz

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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

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