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Math Help - Rewriting a trig expression

  1. #1
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    Rewriting a trig expression

    Write the expression as the sine, cosine, or tangent of an angle

    Problem: cos (pi/2) cos(pi/7) + sin(pi/2) sin(pi/7)

    I start with the cos(u - v) = cos( pi/2 - pi/7) =
    (90 degrees - 25.7) < turned radians into degrees [pi/7 (180/pi)]=about 25.7
    =
    cos(64.3) = .433
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by yeunju View Post
    Write the expression as the sine, cosine, or tangent of an angle

    Problem: cos (pi/2) cos(pi/7) + sin(pi/2) sin(pi/7)

    I start with the cos(u - v) = cos( pi/2 - pi/7) =
    (90 degrees - 25.7) < turned radians into degrees [pi/7 (180/pi)]=about 25.7
    =
    cos(64.3) = .433
    you were not asked to evaluate it. just write it as the cosine of an angle. you get \cos \left( \frac {\pi}2 - \frac {\pi}7 \right) = \cos \frac {5 \pi}{14}
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