先化简再求值(x-y)(x+y)-(x-2y) 的完全平方+x(3x-5y)-(x-y)(x-2y),其中x=1/2 y=-1/2

解(x-y)(x+y)-(x-2y)²+x(3x-5y)-(x-y)(x-2y)=(x²-y²)-(x²-4xy+4y²)+(3x²-5xy)-(x²-3xy+2y²)=(x²-x²+3x²-x²)+(-y²-4y²-2y²)+(4xy-5xy+3...