# How do you find the missing value to create a perfect square trinomial for x^2+8x?

Jul 6, 2018

$+ 16$

#### Explanation:

${\left(x + a\right)}^{2} = {x}^{2} + 2 a x + {a}^{2}$

$\text{compare with } {x}^{2} + 8 x$

$2 a = 8 \Rightarrow a = \frac{8}{2} = 4$

$\text{hence } {x}^{2} + 8 x + {4}^{2} = {x}^{2} + 8 x \textcolor{red}{+ 16} = {\left(x + 4\right)}^{2}$