Answer
To complete the square of $x^2-4x$, add $4$.
Work Step by Step
To complete the square of $x^2-4x$, we must add half of the coefficient of x and square it.
So, we would have:
$(\frac{1}{2}\cdot-4)^2$
=$(-2)^2$
=$4$
To complete the square of $x^2-4x$, add $4$.
