Correct answer only what number needs to be added to both sides of the equation in order to complete the square? x^2 − 18x = 17

Given equation: x^2 − 18x = 17

For completing square method, You have to add something to both sides, so that the LHS becomes a perfect square.

LHS = x^2 - 18x

= (x)^2 - 2 × x × 9 + ___

To make it perfect square,
= (x)^2 - 2 × x × 9 + (9)^2

= (x - 9)^2

So whole equation becomes:

x^2 − 18x + 9^2 = 17 + 9^2

=> x^2 − 18x + 81 = 17 + 81