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Pre-calculas Math

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how to find the exact value of: cos(9*pi/12)*cos(5*pi/12)+sin(9*pi/12)*sin(5*pi/12)

  • Pre-calculas Math - ,

    9pi/12 should be converted into degrees. The value of pi is 180 so all you do is 180 times 9 divided by 12 and then take the cosine of that value.

  • Pre-calculas Math - ,

    cosx cosy + sinx siny = cos(x-y)

    so, what we have here is

    cos(9π/12 - 5π/12) = cos(4π/12) = cos π/3 = 1/2

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