Question

When solving x2 - 12x = -13 by completing the square, what value is added to both sides of the equation? (3 points)
Answer

-6

6

36

144

Answer 1

36 because by adding i can factor and get the square to be (x-6)^2

Answer 2

a^2 + 2a + 1 = (a + 1)^2
x^2 + 6x + 9 = (x + 3)^2
x^2 - 18x + 81 = (x - 9)^2
The third coefficient (1, 9, 81 above) is the square of half of the middle coefficient
(2/2)^2 = 1^2 = 1
(6/2)^2 = 3^2 = 9
(-18/2)^2 = (-9)^2 = 81