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!

Confused about integral

  1. Jun 18, 2013 #1
    The integral is in the attachment.

    Why is the indefinite integral not equal to...
    et(i - 1)/(i - 1) + C

    Because d/dt[et(i - 1)/(i - 1) + C] = et(i - 1)
     

    Attached Files:

  2. jcsd
  3. Jun 18, 2013 #2

    Curious3141

    User Avatar
    Homework Helper

    If ##i## represents the square root of minus 1, then your answer is right, and the integral in the attachment is wrong. Where did you get that from?

    But you should put ##\frac{1}{1-i}## in the form of ##a+bi## in the final answer.
     
  4. Jun 20, 2013 #3
    It seems that what ever calculated that didn't identify the t in the exp(...) and the t in dt. It is either bad notation or plain wrong.
     
  5. Jun 20, 2013 #4
    Don't trust wolframalpha blindly. It has some funny ways of guessing what you mean, and in this case it guesses completely wrong.
     
  6. Jun 20, 2013 #5
    I was indeed able to reproduce the (wrong) result on WA. What you've done is *not* put an asterisk between t and (i-1) in the exp(). This means that WA thinks the t in the exp is maybe some kind of function t(x) [evaluated at x=i-1] and you're integrating wrt. some other variable t.
    In short, if you write "int exp(t*(i-1)),t" and "int exp(t(i-1)),t" you get different results.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted