Question:
Factorize:
$a b\left(x^{2}+y^{2}\right)-x y\left(a^{2}+b^{2}\right)$
Solution:
We have:
$a b\left(x^{2}+y^{2}\right)-x y\left(a^{2}+b^{2}\right)=a b x^{2}+a b y^{2}-a^{2} x y-b^{2} x y$
$=\left(a b x^{2}-a^{2} x y\right)-\left(b^{2} x y-a b y^{2}\right)$
$=a x(b x-a y)-b y(b x-a y)$
$=(b x-a y)(a x-b y)$