Which of the following correctly lists the critical numbers of X^2 - X - 20 < 0

Question

A: -5,4

B: 20, -1

C: 1, -20

D: - 4, 5

Answer 1

The key to finding the critical values is factoring. If you factor the left side you get:

(x-5)(x+4)<0

Set each factor equal to zero and solve.

x-5=0

Add 5 to both sides and simplify

x-5+5=0+5

x=5

x+4=0

Subtract 4 from both sides and simplify

x+4-4=0-4

x=-4

The correct answer is D