先化简再求值 x的平方-8x+16/x的平方-16 其中x=5 x的平方-2x/2y-2x-xy 其中x=-1 y=2

1)
x²-8x+16/x²-16
=x²+8+16/x²-8-8x-16
=(x+4/x)²-8(x-3)
=(5+4/5)²-8(5-3)
=(5+4/5)²-4²
=(5+4/5-4)(5+4/5+4)
=441/25
=17又16/25
2)
x²-2x/2y-2x-xy
=x²-2x+1-1-x(y+1/y)
=(x-1)²-x(y+1/y)-1
=2²+2+1/2-1
=5又1/2