Question

化简求值:(x-y)的平方+(x+y)(y-x)-2x(1-y),期中x=1,y=-2

Answer 1

(x-y)²+(x+y)(y-x)-2x(1-y)

=(x²-2xy+y²)+(y²-2x²)-(2x-2xy)

=x²-2xy+y²+y²-2x²-2x+2xy

=-x²+2y²-2x

=-1²+2×(-2)²-2×1

=-1+8-2

=5