Solve a quadratic equation by completing the square

Question

Solve x^2 -16x = -15 by completing the square

Answer 1

x^2 -16x = -15

x^2 -16x + (-8)^2 = -15 + (-8)^2 Add (-16/2)^2, or (-8)^2, to each side

(x-8)^2 = -15 + (-8)^2 Write left side as the square of a binomial

(x-8)^2 = 49 Simplify the right side

x-8 = +/-7 Square root both sides

x = 8 +/-7 Add 8 to both sides

x = 15 or -1

Answer 2

x² -16x = -15

x² - 16x + 8² = -15 + 8²

(x - 8)² = 49

x - 8 = ±7

x = 8 ± 7