Question

factor to find zeros of y=x^2+4x-21

Answer 1

for its zeros, value of y=0
so
x^2 + 4x - 21 = 0
x^2 + 7x - 3x - 21 = 0
x(x + 7) -3(x + 7) = 0
(x - 3)(X + 7) = 0
if x - 3 = 0, then x = 3
if x + 7 = 0, then x = -7

so the zeros of y are 3 and -7