-x^2y+2xy-y
=-y(x^2-2x+1)
=-y(x-1)^2
9a^2-6ab+b^2
=(3a-b)^2
a^2-4a-12
=(a-6)(a+2)
a^2+8a-9
=(a+9)(a-1)
49x-m^2x
=x(49-m^2)
=x(7-m)(7+m)