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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


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    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.
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