1、(a+b)(a-b)+c(2b-c) =a^2-b^2+2bc-c^2=a^2-(b-c)^2=(a+b-b)(a-b+c)2、4x^2+4xy+y^2-4x-2y+1=0(2x+y)^2-2(2x+y)+1=0(2x+y-1)^2=02x+y-1=02x+y=1所以2x^2+3xy+y^2-x-y =(2x+y)(x+y)-x-y=1*(x+y)-x-y=x+y-x-y=0