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Math Help - Trigonometric Function

  1. #1
    Junior Member
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    Post Trigonometric Function

    Hi,
    I don't understand this well.
    It says:
    use the value of the trigonometric function to evaluate the indicated functions.
    cos t = 4/5
    a) cos(pi - t)
    b) cos(t + pi)

    Can somebody help? Thank you
    Isabel
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by cuteisa89 View Post
    Hi,
    I don't understand this well.
    It says:
    use the value of the trigonometric function to evaluate the indicated functions.
    cos t = 4/5
    a) cos(pi - t)
    b) cos(t + pi)

    Can somebody help? Thank you
    Isabel
    we will use the double angle formulas for cosine, these are:

    cos(A + B) = cosAcosB - sinAsinB
    cos(A - B) = cosAcosB + sinAsinB

    cos t = 4/5
    a) cos(pi - t)
    cos(pi - t) = cos(pi)cos(t) + sin(pi)sin(t) = (-1)(4/5) + 0 = -4/5

    cos t = 4/5
    b) cos(t + pi)
    cos(t + pi) = cos(t)cos(pi) - sin(t)sin(pi) = (4/5)(-1) - 0 = -4/5
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