1题：5/x-5/y=5/xy
(5y-5x)/xy=5/xy
5y-5x=5
y-x=1
y=1+x
2题同1楼.
3题：x-1/x÷(1-1/x)=1
x-1/x÷(x-1)/x=1
x-1/(x-1)=1
(x²-x-1)/x-1=1
x²-x-1=x-1
x²-2x=0
x1=0(舍去),x2=2
4题：-2/x-2-x=1
2/x+x+3=0
x²+3x+2=0
(x+1)(x+2)=0
x1=-1,x2=-2
5题：原式=(1+4/a-2)÷1-2
=1+4/a-4
=4/a-3
6题：原式=3-a/2b×b/a×b/a
=3-b/2a