Question

What number must you add to complete the square? x^2 + 8x = -3

Answer 1

x^2 + 8x = -3
x^2 + 8x + 16 = -3 + 16
using a^2 + 2 a b + b^2 = (a+b)^2

x^2 + 8x + 16 = 13

(x +4)^2 = 13

answer : 16 is the number you must add to complete the square