# Thread: Find x as a function of y

1. ## Find x as a function of y

I have to express x as a function of y in the equation:

y=x/(1-x)

The back of the book says that the answer is y/(1+y). I'm really stuck on how they got there.

2. Originally Posted by blackdragon190
I have to express x as a function of y in the equation:

y=x/(1-x)

The back of the book says that the answer is y/(1+y). I'm really stuck on how they got there.
y(1 - x) = x

=> y - yx = x

=> y = x + yx = x(y + 1)

=> y/(y + 1) = x.

3. Originally Posted by blackdragon190
I have to express x as a function of y in the equation:

y=x/(1-x)

The back of the book says that the answer is y/(1+y). I'm really stuck on how they got there.
I'll explain what he did^^^ Basically "x is a function of y" means the value of x depends on the value of y.

The equation y=x/(1-x) is solved for y, and you can't determine what the value of x would be if you were to know y. So all you do is solve for x by moving everything around as shown in the post above.

properly it would be $\displaystyle f(y)=y/(y+1)$