Find the positive and negative domains of the function below:
y=21x2−2
Then determine for which values of x the following is true:
f(x) > 0
To solve for the positive and negative domains of the function y=21x2−2, we will go through the following steps:
- Step 1: Find the roots of the equation by setting the function equal to zero: 21x2−2=0.
- Step 2: Solve 21x2=2, which simplifies to x2=4. Taking the square root of both sides gives x=2 or x=−2.
- Step 3: Test intervals between the roots (−∞,−2), (−2,2), and (2,∞) to determine where the function is positive.
Now, let's determine which intervals yield positive values:
For x<−2, pick x=−3 and plug into the function: y=21(−3)2−2=21(9)−2=4.5−2=2.5, which is positive.
For −2<x<2, pick x=0: y=21(0)2−2=−2, which is negative.
For x>2, pick x=3: y=21(3)2−2=21(9)−2=4.5−2=2.5, which is positive.
Thus, the function y=21x2−2 is positive for x>2 or x<−2.
Therefore, the solution is x>2 or x<−2.