題目應(yīng)是　已知,(x-x的平方)加(x的平方-y)等于1,求代數(shù)式二分之一(x的平方+y的平方)-xy
(x-x的平方)＋(x的平方-y)等于1,
x-x^2+x^2-y=1
x-y=1
代數(shù)式二分之一(x的平方+y的平方)-xy
=1/2(x^2+y^2)-xy
=1/2(x^2+y^2-2xy)
=1/2(x-y)^2
=1/2*1^2
=1/2