I need to check my answer on this practice problem

Question

Solve for x in the equation

 

x^2 -7x-8=0

 

A. (-1,-8)

B. (1,-8)

C. (-1,8)

D. (1,8)

 

I think the answer is C.

Answer 1

 x² - 7x - 8 =0 


To solve for this you want two factors of 8 that when added together is -7 and when multiplied is -8. 

Given the multiple choice we know the correct factors are 1  and 8. We also know that one of the terms must be negative, that way you'll have to numbers that multiply to -8.

So it's either -1 and 8 or 1 and -8.  Since 1 + -8 = -7, We know that the correct choice is 1, -8 or B.