Question

How do you find the missing value to complete the square `x^2+2x`?

Answer 1

`(x+a)^2 = x^2+2ax+a^2`

We want `2ax` to match `2x`, so `a=1` and the missing value is `a^2 = 1^2 = 1`

`x^2+2x+1 = (x+1)^2`