Question

先化简y/x+y - y/x-y - x²/y²-x² 再求值，其中y/x=5/3

先化简y/x+y - y/x-y - x²/y²-x² 再求值，其中y/x=5/3。。

Answer 1

y/x=5/3
5x=3y
y=(5/3)x
y²=(25/9)x²

原式=y(x-y)/(x+y)(x-y)-y(x+y)/(x+y)(x-y)+x²/(x+y)(x-y)
=(xy-y²)/(x+y)(x-y)-(xy+y²)/(x+y)(x-y)+x²/(x+y)(x-y)
=((xy-y²-xy-y²+x²)/(x+y)(x-y)
=(x²-2y²)/(x²-y²)
=[x²-2(25/9)x²]/[x²-(25/9)x²]
=(-41/9)x²/(-16/9)x²
=41/16

Answer 2

y(x+y)+(x+y)(x-y)-x的2次方
=(x+y)(y+x-y)-x的2次方
=x(x+y-x)
=xy
其中=x-2,y=1/2
所以=-1

Answer 3

y