Question

What are the zeros of f(x) = x2 + x – 30?

A. x = –6 and x = 5
B. x = –5 and x = 6
C. x = –15 and x = 2
D. x = –2 and x = 15

Answer 1

Answer A is correct. (x + 6)(x - 5) = x^2 + x - 30.

Explanation:

Note that -30 = (-5)(6) and (5)(-6). This quadratic can be factored easily:

x^2 + x - 30 = (x + 6)(x - 5) is correct because 6x - 5x = x, the middle term of x^2 + x - 30.

Setting each factor equal to zero, one by one, we get:

x + 6 = 0 => x = -6, and x - 5 = 0 => x = 5

Answer A is correct.

Answer 2

When you factor our f(x)=x^2+x-30, you get (x+6)(x-5). In order to get your zeroes you need to plug in values that would make each of those two parentheses equal to zero. So in this case since -6+6=0 and 5-5=0, your zeros would be x=-6 and x=5.