#### Answer

$r^2-2r+1$

#### Work Step by Step

We start with the given expression: $(r-1)^2$
To simplify an algebraic expression, we must eliminate any parentheses and combine like terms.
We expand the squared term:$(r-1)(r-1)$
We apply the distributive property to multiply the binomials: $r^2-r-r+1$
We combine the like terms by subtracting: $r^2-2r+1$