Question

N Squared - N = 90
N =?

Answer 1

n^2 - n = 90
n^2 - n - 90 = 0
(n - 10)(n + 9) = 0

n - 10 = 0
n = 10

n + 9 = 0
n = -9

answer is : n = 10 and n = -9