Where Does Equation (3) in Kittel's Chapter 5 Come From?

[ehrenfest]

[SOLVED] kittel chapter 5

Homework Statement

This question refers to Kittel's solid-state physics book.

Where does equation (3) come from?

EDIT: never mind

Homework Equations

The Attempt at a Solution

 

[neelakash]

ehrenfest,you should sincerely show your problem and whatever you have thought in this homework help section.We all do it.May be that it is not a homework problem...but understanding the concept yourself is also a way of learning physics.So,better you think over the problem and inform us regarding the details...where the dispute is.

Since, I am not a moderator,possibly I am not the correct man to say this to you.In fact, I too reply to posts very rarely...So take it as a suggestion,not order.