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Math Help - Please check my work...

  1. #1
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    Please check my work...

    Hi,

    136.6025404sin30 = 68.30127019 according to my calculator. However, my teacher has marked my work and says it equals 68.20 rounded to 2 decimal places.

    Can someone please check and see what they get? I can't see why our answers differ.

    Thanks
    Splint
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  2. #2
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    mr fantastic's Avatar
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    Quote Originally Posted by Splint View Post
    Hi,

    136.6025404sin30 = 68.30127019 according to my calculator. Mr F says: Correct.

    However, my teacher has marked my work and says it equals 68.20 rounded to 2 decimal places.

    Can someone please check and see what they get? I can't see why our answers differ.

    Thanks
    Splint
    Where has 136.6025404sin30 come from? Perhaps the error, if any, is in this expression rather than in its value ....
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  3. #3
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    Quote Originally Posted by mr fantastic View Post
    Where has 136.6025404sin30 come from?
    Thanks for your reply Mr Fantastic, 136.6025404 is the length of the hypotenuse and 30 is the angle in degrees which, when calculated as shown above produces the length of the opposite side.

    Have a nice day...
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  4. #4
    MHF Contributor harish21's Avatar
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    Quote Originally Posted by Splint View Post
    Hi,

    136.6025404sin30 = 68.30127019 according to my calculator. However, my teacher has marked my work and says it equals 68.20 rounded to 2 decimal places.

    Can someone please check and see what they get? I can't see why our answers differ.

    Thanks
    Splint
    It should be 68.30 because sin30 = 1/2, and 136.6025404 * 1/2 = 68.3012702

    It would be easier to spot your problem if you posted the entire question!
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  5. #5
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    Quote Originally Posted by harish21 View Post
    It would be easier to spot your problem if you posted the entire question!
    The question shows a right angle triangle where the opposite side is unknown. There is a line drawn from one corner of the triangle which makes another triangle within the right angle triangle, the hypotenuse is a common side of both triangles, part of the adjacent side is common to both triangles and the opposite side is exclusive to the right angle triangle. The sine rule is used to find the length of the hypotenuse, which in turn is used to find the length of the opposite side. I hope that's not too confusing, a picture would be much easier.


    h/sin(135) = 50/sin(15)

    hsin(15) = 50sin(135)

    h = 50sin(135)/sin(15)

    h = 136.6025404 (hypotenuse)

    136.6025404sin(30) = 68.30127019 (opposite side length)

    Having said all that I suspect my teacher has simply made a mistake. I'll send her an email and ask her to check it again, hopefully she'll have time.
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