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Calculators Ti-89 Differing Answers from Integration

  1. Aug 30, 2012 #1
    I am running into an interesting problem on my ti-89 and was wondering if anyone could explain the reason for the following.

    I am attempting to solve the following:
    [tex] M=\int_{x}^{y}sin(\theta )*(r-a*cos(\theta ))d\theta [/tex]

    r = 0.14
    a = 0.09

    x = 0 deg
    y = 120 deg

    The calculator gives me an answer of
    [tex] M = 10.09838 [/tex]
    This answer is incorrect, so I verified that the ti-89 was in degrees (it was) and decided to try the problem in rads instead to see if it is still incorrect.

    now where,
    x = 0 rad
    y = 2*pi/3

    I get a correct answer of
    [tex] M = 0.17625 [/tex]

    What is going on here?
    Last edited: Aug 30, 2012
  2. jcsd
  3. Aug 30, 2012 #2


    Staff: Mentor

    your integral as written is radian based.
    take your 10. 098 answer and divide by 57 degrees (1 rad) and you would get the second answer
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