#### Answer

$$(m-n)(m-n)$$

#### Work Step by Step

$m^{2}-2mn+n^{2}$
Step 1
Open 2 parenthesis, each starts with the square root of the first number. In this case $\sqrt m^{2}$$ = m$
Step 2
Find 2 numbers or variables that:
- Multiplied by each other give you the last term: $n^{2}$
- Added (if the middle sign is positive) or subtracted (if the middle sign is negative) give you the middle term $2n$.
(NOTE: It's just 2n)
In this case those numbers or variables are $n$ and $n$.
Step 3
Write the solution.
The sign of the first parenthesis is the first sign in the original polynomial and the sign in the second parenthesis is the product of both signs in the polynomial.
$(m-n)(m-n)$