1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: What am I doing wrong with this simple integral?

  1. Oct 9, 2006 #1
    I want to integrat x^-2 between -1 to 1. The answer shouldn't exist (should probably be something divided by 0) because the area is infinite between -1 to 1. But I integrate, and I get -x^-1 from -1 to 1. I then plug the bounds in and I get: [-(1)^-1] - [-(-1)^-1] which is -1 -1 or -2. What am I doing wrong?
  2. jcsd
  3. Oct 9, 2006 #2
    Not true. You're right with your answer. One thing you will learn with integrals is that an infinite jump at any particular point in a function f(x) may correspond to a finite jump in its integral.
    Last edited by a moderator: Oct 9, 2006
  4. Oct 9, 2006 #3
    Why is the answer negative? I attached a picture of the graph, it still looks like it should be infinite to me.

    Attached Files:

  5. Oct 9, 2006 #4
    Ok my apologies. You were correct in your arithmetic, but your answer is complete garbage. As far as I know you cannnot integrate over that interval. There are however cases where a function "blows up" but has a finite integral, so you must be careful (the only case I know of however is the dirac delta function, whose integral is 1 over infinite limits)
    Last edited by a moderator: Oct 9, 2006
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook