Question

Solve of x in the proportion 3x/3x-36 = -1/x
A. x=3 and x=-4
B. x=-3 and x=4
C. -3
D. -12

Answer 1

3x/(3x - 36) = -1/x
3x/(3(x - 12)) = -1/x
x/(x - 12) = -1/x
x^2/(x-12) = -1
x^2 = -(x - 12)
x^2 + x - 12 = 0
(x + 4)(x - 3) = 0

thus (x + 4) = 0 or (x - 3) = 0
equivalently, x = -4 or x = 3

A.