=(x-y)^3+4xy(x-y)
=(x-y)[(x-y)^2+4xy]
=(x-y)(x+y)^2a平方bc-3a平方c平方+2abc-6ac平方a平方bc-3a平方c平方+2abc-6ac平方=a^2c(b-3)+2ac(b-c)=ac(bc-3c+2b-2c)=ac(bc-5c+2b)