Question

x^4-1 factorised the sum
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Answer 1

x^4-1

=(x^2-1^2)^2

=(x^2)^2+(1^2)^2-2x^21^2

=x^4+1-2x^2

=x^4-x^2-x^2+1

=x^2(x^2-1)-1(x^2-1)

=(x^2-1)(x^2-1)