How do you find the inverse of $f(x) = x / (x + 8)$ ?

Question

1359 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2015-11-22T00:43:31

Let $y = f(x)$ and solve for $x$ to find:

$f^(-1)(y) = (8y)/(1-y)$

$y = f(x) = x/(x+8) = (x+8-8)/(x+8) = 1-8/(x+8)$

Hence (adding $8/(x+8)-y$ to both ends):

$8/(x+8) = 1 - y$

Hence (multiplying both sides by $(x+8)/(1-y)$ ):

$x+8 = 8/(1-y)$

So:

$x = 8/(1-y) - 8 = 8/(1-y) - (8-8y)/(1-y) = (8y)/(1-y)$

So:

$f^(-1)(y) = (8y)/(1-y)$

How do you find the inverse of f(x) = x / (x + 8)f(x) = x / (x + 8)?