Answer
Constant $=64$.
Perfect square trinomial $=x^2-16x+64$.
Factor form $=(x-8)^2$.
Work Step by Step
The given expression is in the form of $x^2+bx$, where $b=-16$.
Add $\left (\frac{b}{2} \right )^2$ to complete the square.
Therefore we add
$=\left (\frac{-16}{2} \right )^2$
$=\left (-8 \right )^2$
$=64$
Hence, the perfect square trinomial is
$=x^2-16x+64$
Perfect square in the factor form is
$=\left (x+\frac{b}{2} \right )^2$
$=(x+\frac{-16}{2})^2$
$=(x-8)^2$
