Answer
$$(x-1)^2 .$$
Work Step by Step
The polynomial $ x^2-2x+1 $ is a complete square since it is of the form $a^2-2ab+b^2=(a-b)^2$. Thus, by putting $a=x$, $b=1$, we have
$$ x^2-2x+1=(x-1)^2 .$$
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