Question

For what values of x is x^2-36=5x true?

A. -9 and -4
B. -4 and 9
C. 4 and -9
D. 9 and 4

Answer 1

x^2-36=5x

x^2-5x-36=0

x^2-9x+4x-36=0

x (x-9)+4(x-9)=0

(x+4)(x-9)=0

x=-4,9

Therefore, option b is correct.

Answer 2

${x}^{2} - 5x - 36 = 0 \\ {x}^{2} - 9x + 4x - 36 = 0 \\ x(x - 9) + 4(x - 9) = 0 \\ (x - 9)(x + 4) = 0 \\ x = 9 \: or \: x = - 4$