Question

What must be added to the expression x^2 - 18x to make it a perfect square?

Answer 1

+ 81

Explanation:

Given

x² - 18x

To complete the square

add ( half the coefficient of the x- term )² to x² - 18x

x² + 2(- 9)x + (- 9)²

= x² - 18x + 81

= (x - 9)² ← perfect square