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
