Answer
$y=-5$
Work Step by Step
$y^{2}+10y+25=0$
Use the quadratic formula to solve this equation. The formula is $y=\dfrac{-b\pm\sqrt{b^{2}-4ac}}{2a}$. For this equation, $a=1$, $b=10$ and $c=25$
Substitute:
$y=\dfrac{-10\pm\sqrt{10^{2}-4(1)(25)}}{2(1)}=\dfrac{-10\pm\sqrt{100-100}}{2}=...$
$...=\dfrac{-10\pm\sqrt{0}}{2}=\dfrac{-10}{2}=-5$