Question

先化简再求值2(x+y)-(2x-y)(x-y),其中x=1,y=-1

Answer 1

2(x+y)-(2x-y)(x-y)
=2(x+y)-(x+x-y)(x-y)
=2(x+y)-x(x-y)-(x-y)^2
x+y=0
x-y=2
则 2(x+y)-(2x-y)(x-y)=2(x+y)-x(x-y)-(x-y)^2
=-2-4
=-6

Answer 2

2(x+y)²-(2x-y)(x-y),
=2x²+4xy+2y²-2x²+3xy-y²
=7xy+y²
=7*1*(-1)+(-1)²
=-7+1
=-6