主項變換~

You are right...
z=mx+ny/m+n
z(m+n)=mx+ny
zm+zn-ny-mx=0
m(z-x)+n(z-y)=0
n(z-y)=-m(z-x)
n=-m(z-x)/(z-y) or
n=[m(x-z)]/(z-y) or
n=zm-mx/y-z

上二位are also right...

錯...
z=mx+ny(over)m+n [n]
z(m+n)=mx+ny
zm+zn=mx+ny
zm+zn-zn-mx=mx+ny-mx-zn
zm-mx=ny-zn
zm-mx=n(y-z)
zm-mx
---------=n
y-z

我吾係好知= =" s o r ...
我計倒嘅係咁...

z=(mx+ny)/(m+n) [n]
z(m+n)=mx+ny
zm+zn=mx+ny
zn-ny=mx-zm
n(z-y)=m(x-z)
n=[m(x-z)]/(z-y)

我個答案同你個答案有d吾同= ="
我計錯吾好怪我... s o r ...