Question

(a2-b2)(a2+b2)-(a2-b2)

Answer 1

$(a^{2}-b^{2})(a^{2}+b^{2})-(a^{2}-b^{2})$
$= (a^{2})^{2}-(b^{2})^{2}-(a^{2}-b^{2})$
$= a^{4}-b^{2}-(a^{2}-b^{2})$
$= a^{4}-b^{4}-a^{2}+b^{2}$

Hope this may help you.