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March 25, 2017

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How do I do these type of problems

find the exact value. Do not use a calculator

cos 7pi

  • Calculus (trig stuff) - ,

    2&pi is one full rotation around the circle, so you can think of 2&pi as being the same as 0. so 7 pi is the same as going around the circle 3 full times with 1&pi left over, to figure this out exactly you can do the following:

    (7/2) = 3 +1/2
    the 3 is how many times we went 2&pi around the circle, and what we have left is (1/2)*2&pi or 1&pi

    cos(&pi) = -1


    To do another example

    sin((9/2)&pi)

    well (9/2)/2 is the same as (9/2)*(1/2)=(9/4)

    we get 2 + 1/4 so we get 2 full rotations plus 1/4 of a full rotation. A full rotation is just 2&pi so:

    2&pi*(1/4) = &pi/2

    sin(&pi/2) = 1

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