Let $f(x) = x^2 - 4\sqrt{x} + 1$. What is $f(f(4))$?
To find $f(f(4))$, I need to first find $f(4)$ and then plug it back into $f(x)$. So, $f(4) = 4^2 - 4\sqrt{4} + 1 = 16 - 8 + 1 = 9$. Now, $f(f(4)) = f(9) = 9^2 - 4\sqrt{9} + 1 = 81 - 12 + 1 = 70$.

