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February 7th, 2013, 08:06 AM   #1
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Cosine graph, sine graph basics confusion

I have gotten a bit confused to why these rules work for sine and cosine graphs. My confusion stems from I can't really see what they mean literally.

The rules are: sin x = sin(180+x) and cos x = cos(360-x). I know it has something to do with symmetry, but I can't seem to connect the dots.

Thanks in advance.
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February 7th, 2013, 10:07 AM   #2
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The first rule should be sin x = -sin(180+x). Have you looked at the graphs of sin(x) and cos(x) to see what symmetries exist? Alternatively, consider how these functions are defined in relation to the unit circle and what symmetries of the unit circle correspond to the two rules.
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