Question

(x-y) (x-2y)+(x+2y) (x-3y)-2(x-3y) (x-4y)=

Answer 1

(x-y) (x-2y)+(x+2y) (x-3y)-2(x-3y) (x-4y)

=(x-y) (x-2y)+（x-3y)[(x+2y) -2(x-4y)]

=(x-y)(x-2y)+(x-3y)[10y-x]

=x^2-xy-2xy+2y^2+10xy-3y^2-x^2+3xy

=-y^2+10xy

=y(10x-y)