Question

What value is added to both sides of the equation x2 - 8x = -10 in order to solve by completing the square?

Answer 1

x² - 8x = -10

to have a complete square, we must have this format:

a² + 2ab + b²

a² = x²
2ab = -8x ⇒ 2(x)(-4)
b² = -4² = 16

x² - 8x + 16 = -10 + 16
x² - 8x + 16 = +6
(x-4)² - 6 = 0

Both sides must have an additional value of 16.