Homework Help: L'Hopitals Rule need help with derivatives?

1. Jul 6, 2006

m0286

Question is:
Evaluate the following limits
lim x--> 0 4^x - e^2x / 2x
So i take derivatives
but thats where im confused.... Whats the derivate of 4^x... x4^-x???
and is the derivative of -e^2x -2e^x???
So then that leaves me with 4x^-x -2e^x /2which is 0... so do i do derivatives again??? It seems like the x's wont go away????

Last edited: Jul 6, 2006
2. Jul 6, 2006

StatusX

You can use the chain rule and the fact that the derivative of e^x is e^x to answer both questions. That is, the derivative of e^f(x) is e^f(x)*f'(x). Try to rewrite 4^x as e^f(x). (use logs)

3. Jul 7, 2006

Jameson

$$f(x)=4^x$$
$$\ln(f(x))=x\ln(4)$$
$$\frac{1}{f(x)}*f'(x)=\ln(4)$$

You can take it from there.