# Simple question about using L'Hopital's Rule to solve limits

1. Jul 21, 2010

### Chandasouk

I know L'Hoptal's rule can only be use when you have indeterminate forms and such, but I do not know how to make a limit a fraction sometimes. Take this limit for example:

The limit at which X approaches infinity of (1+$$\frac{1}{x}$$)X

I make y = The limit at which X approaches infinity of (1+$$\frac{1}{x}$$)X

Take the Ln of both sides to get

lny = X*ln(1+$$\frac{1}{x}$$)

which can be rewritten as ln(1+1/x)/(1/x) but how? I get lost in the algebra and don't know how to obtain that.

2. Jul 21, 2010

### Dick

x=1/(1/x).

3. Jul 21, 2010

### Staff: Mentor

Multiplying by x is the same as dividing by 1/x (assuming x is not 0).

4. Jul 21, 2010

### HallsofIvy

One of the things you learned way back in elementary school was "to divide by a fraction, invert and multiply". Dividing by 1/x is the same inverting to get x and then multiplying:
$x ln(1+ 1/x)= ln(1+ 1/x)/(1/x)$

This also works the other way: multiplying by a fraction is the same as dividing by its reciprocal: multiplying by x (which is the fraction x/1) is the same as dividing by its reciprocal, 1/x.

5. Jul 21, 2010

### Chandasouk

Holy crap. Thanks guys. It's weird how I forget simple stuff but can do the "calculus" fine.