How to get all the coefficients of specific powers of x?

Questions
1

Hello
I have a very big and complex expression with variable x. There are different powers of this variable. I need the following thing. I specify the power of x (say, x^2) and write down all the coefficients belonging to x^2 in my expression. I am absolutely new in Mathematic?. So could you just give me corresponding links/references/advices so that I will read it and try?
P.S. To do this job on a sheet of paper is impossible. The expression is rather huge. It is very easy to make a mistake. After each recalculation I get different results…

2

You could use the built in function “Coefficient”.

3

If you go to Help menu - Documentation Center, there is a very useful search capability.
For example, if you type “coefficients” into the search slot near the top of the window,
the first and third hits are very relevant.

DocCntrSearch.jpg
DocCntrSearch.jpg786Ă—375 39.7 KB

Most Mathematica functions have names related to what they are used for.