Work Step by Step
We start by factoring out $x^5$: $x^7-x^5=x^5(x^2-1)$ The polynomial $x^2-1$ is of the form $a^2+2ab+b^2=(a+b)^2$, which is a complete square. That is, we have $$ x^7-x^5=x^5(x^2-1)=x^5(x-1)(x+1) .$$
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