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Math Help - Evaluating with pi?

  1. #1
    Junior Member
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    Oct 2008
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    Evaluating with pi?

    I'm confused on how to complete these kind of problems:

    Evaluate cos 31(pi)/3

    Evaluate sin 15(pi)/4

    How do I do these when pi is involved?


    Also, how would I find a reference angle when pi is involved? Example:

    Find the measurement of the reference angle of an angle measuring 7(pi) /4.
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  2. #2
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    Do you know what a radian is? If not, that's the problem. A radian is another measurement of angles that uses pi. 1(pi) = 180 degrees, (pi)/4 = 45 degrees, etc.

    However, if you do know what radians is, this is how you do it:

    31(pi)/3 is the same as 30(pi)/3 + (pi)/3, which is the same as 10pi + (pi)/3. By seeing it like this you can see that your angle is going to be in the same place as (pi)/3 because every 2(pi) you make a full revolution.

    To find a reference angle it's similar. Draw a coordinate axis and plot your angle 7(pi)/4 by drawing a line. This angle is in the fourth quadrant. The reference angle is then measured from the x-axis. 7(pi)/4 is the equivalent of a "45 degree" angle in the fourth quadrant, so this means your reference angle will be (pi)/4.

    I hope that helps.
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