Final answer to the problem
$\left(m+n\right)^2$
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Step-by-step Solution
Specify the solving method
1
$x+0=x$, where $x$ is any expression
$\left(m+n\right)\cdot \left(m+n\right)$
2
When multiplying two powers that have the same base ($m+n$), you can add the exponents
$\left(m+n\right)^2$
Final answer to the problem
$\left(m+n\right)^2$