Find the positive and negative domains of the function below:
y=(x−31)(−x−241)
Then determine for which values of x the following is true:
f(x) < 0
To solve this problem, we need to find the roots and determine the sign of the function on intervals between these roots:
- Step 1: Find the roots of the quadratic by solving each factor equal to zero.
- Step 2: x−31=0 gives x=31.
Solve −x−241=0 gives x=−241 or x=−49.
- Step 3: This defines the critical points, x=31 and x=−49.
- Step 4: Determine the sign of the function on intervals: (−∞,−49), (−49,31), and (31,∞).
- Step 5: Test points in each interval:
For x<−49, both factors are negative, the product is positive: Interval does not satisfy.
For −49<x<31, signs will vary, and the product is negative: Interval satisfies f(x)<0.
For x>31, both factors are positive, the product is positive: Interval does not satisfy.
Thus, the solution is for values where the product is negative: −241<x<31.
The correct answer choice is therefore Choice 1
x > \frac{1}{3} or x < -2\frac{1}{4}