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Math Help - Trigonometric identity - HELP please

  1. #1
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    Smile Trigonometric identity - HELP please

    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) tan 35 degrees
    Showing the steps you would follow. NOTE: sin^2theta+cos^2theta=1
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  2. #2
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    Quote Originally Posted by GAVREED2 View Post
    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) tan 35 degrees
    Showing the steps you would follow. NOTE: sin^2theta+cos^2theta=1
    First of all, use the Pythagorean Identity to find sin(20) and cos(55).

    Then remember that tan(35) = [sin(35)]/[cos(35)]

    = [sin(55 - 20)]/[cos(55 - 20)]

    Now use the angle sum rule to finish.
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  3. #3
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    I'm not entirely sure why they want you to use the angle sum identities, since there is a shorter way. The denominator cos(35) equals sin(90-35) = sin(55), which is given.

    Likewise, the numerator sin(35) = cos(90-35) = cos(55), which is known after using the Pythagorean identity.
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