• Support PF! Buy your school textbooks, materials and every day products Here!

Cosine question

  • Thread starter Moneer81
  • Start date
159
2
1. Homework Statement
While solving the integral of a wave function,I came across the term cos(n*pi) , where n is an integer. Is that term equal to +1 or -1 (I know that it could be either one depending on whether n is odd or even) but how do I proceed with the integral?


2. Homework Equations

none

3. The Attempt at a Solution

cos (n*pi) is 1 if n is even and -1 if n is odd...but how do proceed?

thanks a lot
 

Answers and Replies

Tom Mattson
Staff Emeritus
Science Advisor
Gold Member
5,474
20
Why does n have to be +1 or -1? Why can't it be 2, for instance?
 
159
2
n could be any integer, but the whole term cos (n*pi) will have to be +1 or -1
 
Tom Mattson
Staff Emeritus
Science Advisor
Gold Member
5,474
20
OK, so you're trying to integrate and you have somewhere a factor of [itex]\cos(n\pi)[/itex], where [itex]n[/itex] is an integer. Is that right? In that case you can just replace [itex]\cos(n\pi)[/itex] with [itex]\pm 1[/itex].

This looks pretty straightforward to me. It might help me understand why this is giving you trouble if you typed out the integral that you are trying to do, what you have done, and where you got stuck.
 
141
0
You can write the term as

[tex]
\cos(n\pi) = (-1)^{n}
[/tex]

It doesn't really help that much, but you see this a lot. Since this is a constant term you can just proceed to perform the integral you want to evaluate.
 

Related Threads for: Cosine question

  • Last Post
Replies
10
Views
907
Replies
3
Views
938
Replies
6
Views
2K
Replies
2
Views
1K
  • Last Post
Replies
3
Views
967
  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
14
Views
20K
  • Last Post
Replies
11
Views
1K
Top