# How do you make x^2 + 10x + c a perfect square?

Remember that the perfect square${\left(x + a\right)}^{2} = {x}^{2} + 2 a x + {a}^{2}$
So if ${x}^{2} + 10 x + c$ is a perfect square then
$2 a = 0$
$\rightarrow a = 5$
and since $c = {a}^{2}$
$c = 25$