Answer:
+ 16
Step-by-step explanation:
x² - 8x = - 10
to complete the square
add ( half the coefficient of the x- term )² to both sides
x² + 2(- 4)x + (- 4) = - 10 + (- 4)²
x² - 8x + 16 = - 10 + 16
thus 16 is added to both sides to complete the square