Complete the square on the following quadratic x^2+18x+7=0 what value is added to both sides of the equation.

X^2 + 18x + 7 = 0

x^2 + 18x = - 7

x^2 + 18x + 81 = - 7 + 81 ... add 81 to both sides

(x + 9) ^2 = 74

x + 9 = sqrt 74

x = - 9 (+-) sqrt 74

x = - 9 + sqrt 74

x = - 9 - sqrt 74

the reason u add 81 to both sides ... u take half of the x term, then square it.

half of 18 is 9 ... 9^2 = 81