2. Well, we can rewrite $5^x$ as $e^{x\cdot \ln 5}$. Now
$\frac{d}{dx} 5^x = \frac{d}{dx} e^{x\cdot \ln 5} = \ln 5 \cdot e^{x\cdot \ln 5} = \ln 5 \cdot 5^x$