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Oct22-11, 10:54 PM
HW Helper
P: 1,663
Use the "double-angle formula" for cosine -- there are three forms of it, but one of the expressions for y = cos(2t) will have a simple connection to x = sin t in the vector equation for r .

(The double-angle formulas for sine and cosine from trigonometry are ones that it are useful to know. They see a lot of application...)