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Math Help - How to calculate magnitude?

  1. #1
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    How to graph trig without a calculator??

    Sorry about the double post, no idea how that happened.

    How to graph trig without a calculator?

    The question:
    Graph the following without using a graphing program:
    y = 2 cos ( 2 x- 900 ) (Thats 90 degrees)

    The lesson I was given contains a very small explanation that is basically useless. So I'm not really sure how to start this..
    Last edited by Urpes; July 22nd 2013 at 02:55 PM. Reason: double post
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  2. #2
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    Re: How to calculate magnitude?

    So y= cos(2(x- 45)). This problem looks like it expects you to know how to work with a "general sinusoidal function". Since cosine of any number lies between -1 and 1, this function will always lie between -2 and 2. Cosine has period 360 degrees but when 2x= 360, x= 180 so this function has period 180 degrees. Finally, cos(0)= 1 and 2x- 90= 2(x- 45)= 0 when x= 45.
    So I would do this: Draw two horizontal lines at y= -2 and y= 2 to give the boundaries. Start at the upper line at x= 45. 45+ 180= 225 so mark (225, 2). The 180 interval divides into 4 sections: 180/4= 45 so at x= 45+ 45= 90, we are at 0, at 90+ 45= 135 down to -2, at 135+ 45= 180, up to 0 again, at 180+ 45= 225 up to 2 again, completing the cycle.
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