Question

What are the solutions to the quadratic equation 3x2 + 15x – 18 = 0?

A. x = –3 and x = 6
B. x = –6 and x = 1
C. x = –2 and x = 9
D. x = –6 and x = 3

Answer 1

First divide by 3 because we don't want any factor in front of the x² when doing factorization:

3x² + 15x – 18 = 0 => x² + 5 - 6 = 0

Then find the two numbers that multiply to -6 and add up to +5:

x² + 5 - 6 = 0 => (x-1)(x+6) = 0

So the solutions are x=1 or x=-6, that's answer B.