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Integration of sine

  1. Oct 21, 2009 #1
    1. The problem statement, all variables and given/known data
    what is the integration of 1/2 sin y dy from 0 to pie/2


    2. Relevant equations
    i know sin y = -cos y (integration)



    3. The attempt at a solution
    from 1/2 sin y dy to (1/2) -cos y then i plot pie/2 and 0
    i got (1/2) [-cos (pie/2) - (-cos 0)] = 0, but the answer is 1/2
    i mean -cos (pie/2) = -1 & cos 0 = 1

    Thank you for helping
     
  2. jcsd
  3. Oct 21, 2009 #2

    Mark44

    Staff: Mentor

    Error in next line. BTW, the name of the Greek letter is pi, not pie. Pie is something you can eat.
    (1/2)[-cos (pi/2) - (-cos 0)] != 0
     
  4. Oct 21, 2009 #3
    i forgot to add this, im trying to find out why the answer is 1/2 and not 0.
     
  5. Oct 21, 2009 #4

    Mark44

    Staff: Mentor

    See post 2. I identified the line where you went wrong.
     
  6. Oct 21, 2009 #5
    but i though the integration of sin y is -cos y?
     
  7. Oct 21, 2009 #6

    Mark44

    Staff: Mentor

    I'm not questioning that. Did you read post 2?
     
  8. Oct 21, 2009 #7
    integration of 1/2sin(y) dy from 0 to pie/2=1/2[-cos(y)] from 0 to pie/2
    =1/2{-cos(pie/2)-[-cos(0)]}
    =1/2{0+1}
    =1/2 [bcoz cos(0)=1 & cos(pie/2)=0]



    :smile:
     
  9. Oct 21, 2009 #8
    k, i got it, i put cos (pi/2) in my calculator but came out to be .9996, so that's why i didn't get the right answer.

    edit. just know why, cause i have the mode under deg so that's why my answer is all mess up.

    thanks everybody
     
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