Question

x^2-4x-21=0 completando cuadrados plis

Answer 1

x^2 - 4x - 21 = 0

x               -7

x               +3

+3x - 7x = -4x

(x-7)(x+3) = 0

x - 7 = 0       x + 3 = 0

x = 7             x = -3