1a
x^2 × (x^2 - 1) - x^2 + 1 = x^2 × (x^2 - 1) - (x^2 - 1) = (x^2 - 1)(x^2 - 1) = (x^2 - 1)^2
=> (x^2 - 1)^2 = 0
=> x^2 - 1 = 0
=> x^2 = 1
=> \(\left[ \begin{array}{l}x=1\\x=-1\end{array} \right.\)
2a
(x - y)(x^2 - xy + y^2) + 2y^3 = x^3 - y^3 + 2y^3 = x^3 + y^3