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Math Help - Hard - Trigonometric function

  1. #1
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    Exclamation Hard - Trigonometric function

    Help me solve this question. Can't seem to grasp the formula


    4)Given that sin 55degrees = 0.819 and cos20degrees = 0.94,
    show how you would use the identities for sin(A+B) and cos(A+B) to find the following:
    a) sin 75degrees
    b) cos 35 degrees
    c) tan 35 degrees
    Showing the steps you would follow. NOTE: sin^2theta+cos^2theta=1
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  2. #2
    MHF Contributor harish21's Avatar
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    Quote Originally Posted by GAVREED2 View Post
    Help me solve this question. Can't seem to grasp the formula


    4)Given that sin 55degrees = 0.819 and cos20degrees = 0.94,
    show how you would use the identities for sin(A+B) and cos(A+B) to find the following:
    a) sin 75degrees
    b) cos 35 degrees
    c) tan 35 degrees
    Showing the steps you would follow. NOTE: sin^2theta+cos^2theta=1
    sin(A+B) = sinAcosB+cosAsinB

    so sin75=sin(55+20)=sin55.cos20+cos55.sin20

    cos(A-B) = cosA.cosB+sinA.sinB

    so cos35= cos(55-20)=cos55.cos20+sin55.sin20
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    Question Thanks

    Thanks for your help again.....Just wondering how you find c) Tan


    Quote Originally Posted by harish21 View Post
    sin(A+B) = sinAcosB+cosAsinB

    so sin75=sin(55+20)=sin55.cos20+cos55.sin20

    cos(A-B) = cosA.cosB+sinA.sinB

    so cos35= cos(55-20)=cos55.cos20+sin55.sin20
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  4. #4
    MHF Contributor harish21's Avatar
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    Quote Originally Posted by GAVREED2 View Post
    Thanks for your help again.....Just wondering how you find c) Tan
    tan(A-B)=\frac{sin(A-B)}{cos(A-B)}

    or

    tan(A-B) = \frac{tanA-tanB}{1+tanA.tanB}
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  5. #5
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    Talking

    Thanks mate! Ur a lifesaver
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