Answer
$x^2+10x+25
\Rightarrow
(x+5)^2
$
Work Step by Step
The third term of a perfect square trinomial is equal to the square of half the coefficient of the middle term. Hence, to complete the square of the given expression $
x^2+10x
,$ the third term must be
\begin{array}{l}\require{cancel}\left( \dfrac{10}{2}
\right)^2\\\\=\left(
5
\right)^2\\\\=
25
.\end{array}
Hence, $
x^2+10x+25
\Rightarrow
(x+5)^2
.$
