Solve y = (1/2)x² - 2: Finding Positive Function Values

Question

Find the positive and negative domains of the function below:

y=12x22 y=\frac{1}{2}x^2-2

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

f(x) > 0

Step-by-Step Solution

To solve for the positive and negative domains of the function y=12x22 y = \frac{1}{2}x^2 - 2 , we will go through the following steps:

  • Step 1: Find the roots of the equation by setting the function equal to zero: 12x22=0 \frac{1}{2}x^2 - 2 = 0 .
  • Step 2: Solve 12x2=2 \frac{1}{2}x^2 = 2 , which simplifies to x2=4 x^2 = 4 . Taking the square root of both sides gives x=2 x = 2 or x=2 x = -2 .
  • Step 3: Test intervals between the roots (,2)(- \infty, -2), (2,2)(-2, 2), and (2,) (2, \infty) to determine where the function is positive.

Now, let's determine which intervals yield positive values:

For x<2 x < -2 , pick x=3 x = -3 and plug into the function: y=12(3)22=12(9)2=4.52=2.5 y = \frac{1}{2}(-3)^2 - 2 = \frac{1}{2}(9) - 2 = 4.5 - 2 = 2.5 , which is positive.

For 2<x<2-2 < x < 2, pick x=0 x = 0 : y=12(0)22=2 y = \frac{1}{2}(0)^2 - 2 = -2 , which is negative.

For x>2 x > 2 , pick x=3 x = 3 : y=12(3)22=12(9)2=4.52=2.5 y = \frac{1}{2}(3)^2 - 2 = \frac{1}{2}(9) - 2 = 4.5 - 2 = 2.5 , which is positive.

Thus, the function y=12x22 y = \frac{1}{2}x^2 - 2 is positive for x>2 x > 2 or x<2 x < -2 .

Therefore, the solution is x>2 x > 2 or x<2 x < -2 .

Answer

x > 2 or x < -2