$\displaystyle \lim_{x \to \infty} $ (4^x + 7^x)^(1/x)

First I took the ln of (4^x + 7^x)^(1/x) to get (4^x + 7^x)/x and derived the top and bottom, so I got a function of

(4^x *ln4 + 7^x *ln7)/(4^x + 7^x)

and I took the derivative of the top and bottom again, but I could tell already that things were going nowhere :/