factorizar os polinomiozz
ax-bx-ay+by
xfa
ax-bx-(ay-by)
x(a-b)-y(a-b)
(a-b)(x-y)
se resuelve ax +bx-ay+by factor comun
(ax-bx)-(ay+by)
x(a+b)-y(a+b)
R// (x-y) (a+b)
