## College Algebra 7th Edition

$(x-1)^{2}(x+1)^{2}$
We treat $x^4$ as $(x^2)^2$ and use the fact that $(a-b)(a+b)=a^2-b^2$: $x^{4}-2x^{2}+1=(x^{2}-1)^{2}=[(x-1)(x+1)]^{2}=(x-1)^{2}(x+1)^{2}$