x²-y/ax-bx+ay-by=?

x²-y/ax-bx+ay-by=?

ax-bx+ay-by
=(ax+ay) - (bx+by)
=a(x+y)-b(x+y)
=(a-b)(x+y)
원식 = (x+y) (x-y) / (a-b) (x+y)
=(x-y)/(a-b)