Question

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

Answer 1

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