# Toronto Math Forum

## MAT334--2020F => MAT334--Lectures & Home Assignments => Chapter 1 => Topic started by: RunboZhang on September 22, 2020, 09:16:34 PM

Title: Question on Textbook Section1.5 The Log Function Example 3
Post by: RunboZhang on September 22, 2020, 09:16:34 PM
Hi everyone, I have went through textbook section 1.5 and found an example quite confusing (pic is attached below). In this example, in order to get the limit (n->∞), we discuss the real part and imaginary part separately. But I don't know how does it solve for the real part. In particular, it says we need to use L'Hopital's rule and we will get x as the result. However, I have been stuck at this computation (the draft in orange color is my computation) and it seems like a dead end. I dont know if I did wrong at the very first step. Besides, when we are using L'Hopital's rule here, are we taking the derivative with respect to n or x? How can we know which is the variable?
Title: Re: Question on Textbook Section1.5 The Log Function Example 3
Post by: Jessica Long on September 22, 2020, 11:01:08 PM
The derivative is with respect to n. I've attached my computation of the limit, it starts off in the same way as yours.

Edit: there should be an n2 in the denominator, but it does not affect the result.