How to get the inverse of this function, when we have qudratic? $$f(x)=-x^2+6x-5$$ 
How do I find the inverse? I tried by making it 
$$y=-x^2+6x-5$$
Then swapping $y$ with $x$, and then solve it for y, but I got $y^2$.
The domain is $x$ greater or equal to $m$, and in this case $m=5$.
After that we need to find the domain of the inverse.

The simplest one is by completing the square
$f(x)=y=-((x-3)^2-4)$,
$4-y=(x-3)^2$,
$x=3\pm\sqrt{4-y}$.
