Answer
$4x$
Work Step by Step
The given expression can be written as:
$=(4x)^2+2(4x)(5y)+(5y)^2$
RECALL:
The perfect square trinomial $a^2+2ab+b^2$ can be factored as $(a+b)^2$.
Factor the trinomial using the formula above with $a=4x$ and $b=5y$ to obtain:
$=(4x+5y)^2$
Thus, the missing expression in the given statement is:
$4x$
