a, x(x-y)+y(x-y)=(x-y)(x+y)

=\(x^2-y^2\)

b, \(x^{n-1}\left(x+y\right)-y\left(x^{n-1}+y^{n-1}\right)=x^{n-1+1}+xy^{n-1}-xy^{n-1}-y^{n-1+1}\)

=x\(^{x^n+xy^{n-1}-xy^{n-1}-y^n}\)

=\(x^n-y^n\)

tl muộn nhưng dễ hiểu hơn câu tl trc