# When solving x^2 – 4x = –7 by completing the square what value is added to both sides of the equation?

Apr 29, 2015

What value needs to be added to ${x}^{2} - 4 x$
${\left(x + a\right)}^{2} = {x}^{2} + 2 a x + {a}^{2}$
We have $2 a x = - 4 x$
$\rightarrow a = - 2$
So ${a}^{2} = 4$
We need to add $4$ to ${x}^{2} - 4 x$ in order to complete the square.