x-y怎么用x+y和y/x表示?

Question

x-y怎么用x+y和y/x表示?

Answer 1

a=x+y,b=y/x
y=bx
所以a=x+bx
x=a/(b+1)
y=ab/(b+1)
所以x-y=a(1-b)/(a+b)
即x-y=(x+y)(1-y/x)/[(x+y)+y/x]