初一数学乘法公式有关题已知X(X-1)-(X^2-y)=-2.求x^2+y^2/2-xy的值x^2+y^2/2-xy是先除以2再减xy
问题描述：
初一数学乘法公式有关题
已知X(X-1)-(X^2-y)=-2.求x^2+y^2/2-xy的值
x^2+y^2/2-xy是先除以2再减xy
答
x^2-x-x^2+y=-2
y-x=2
所以x-y=2
(x^2+y^2)/2-xy
=(x^2-2xy+y^2)/2
=(x-y)^2/2
=4/2
=2
5
答
x^2-x-x^2+y=-2
y-x=2
所以x-y=2
(x^2+y^2)/2-xy
=(x^2+y^2)/2-2xy/2
=（x^2-2xy+y^2)/2
=（x-y)^2/2
=2^2/2=2 也许你会明白点啊
答
首先,x^2-x-x^2+y=-2
y-x=-2
x-y=2
所以 (x-y)^2=2^2=4
=x^2+y^2-2xy
(x-y)^2/2=4/2=2
=(x^2+y^2)/2-xy
即(x^2+y^2)/2-xy＝2