Maths!!!

你地有無看清楚問題? 根本就是錯問題..

y = c+ a-x/x
xy=c+a-x
xy+x=c+a
x(y+1)=c+a
x=(c+a)/(y+1)

y = c+ a-x/x
xy=c+a-x
xy+x=c+a
x(y+1)=c+a
x=(c+a)/(y+1)

The question has problem
if
y = c+(a-x)/x
then
y-c=(a-x)/x
x(y-c)=a-x
xy-xc+x=a
x(y-c+1)=a
x=a/(y-c+1)

so the pervious answer is wrong

but if y = a- x/x
then y=a, x can be any number except 0

y= c + a-x/x
xy = c+a-x
xy - (a-x) = c
x ( y - a )= c
x = c / y-a