Answer
$4a^2+4ab+b^2$.
Work Step by Step
The given expression is
$=(2a+b)^2$
Use formula $(a+b)^2=a^2+2ab+b^2$.
We have $a=2a$ and $b=b$.
$=(2a)^2+2(2a)(b)+(b)^2$
Simplify.
$=4a^2+4ab+b^2$
Hence, the product is $4a^2+4ab+b^2$.
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