finding the inverse of function. the domain is given and the question requires to find the inverse. Find the inverse of the function.
$$f(x)=x^2 + 4x$$
Domain: $x \geq -2$
I have done: 


*

*$X = y^2 + 4y$

*$X - 4y = y^2$

*$\sqrt{X - 4y} = y$
My answer:  $f^{-1}(x) = \sqrt{X - 4x} $
Real answer: $f^{-1}(x) = -2 \pm \sqrt{x + 4}$

$y=x^2+4x \Rightarrow x^2+4x-y=0 \Rightarrow x=\frac{-4\pm\sqrt{16+4y}}{2}$ 
