What number must you add to complete the square x2+12x=40

36

Step-by-step explanation:

Find a value that is equal to the square of half of b, coefficient of x

(b/2)^2 = (12/2)^2

(6)^2

Add (6)^2 to both sides.

x^2+12x+(6)^2 =40 +(6)^2

x^2+12x+36=40+36

x^2+12x+36= 76

Factor the perfect trinomial square into (x+6)^2

(x+6)^2= 76

Thus 36 must be added to both sides to complete the square