$$\cos(3\pi/2 - a) = -\sin(a)$$
According to an answer to one of the questions in my book that's true, but come up with that? $$\cos(\pi/2 - a) = \sin(a),$$ but this is $3\pi/2$. Do you just ignore if $\pi$ is multiplied by anything or?
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That's because $\cos{(x\pm y)}=\cos{x}\cos{y}\mp\sin{x}\sin{y} $ – CIJ Mar 27 '15 at 05:34
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This answer may help your understanding. – Blue Mar 27 '15 at 05:43
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Does it help to picture a diameter drawn through the unit circle? If it crosses the circle at $(x,y)$, it should also cross at $(-x,-y)$ and the 2 radii are separated by 180 degrees. – Mike Mar 27 '15 at 05:44
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Hmm... I think maybe I get it somewhat. – windy401 Mar 27 '15 at 05:48
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@windy401 Did the answer I provided helped? Should you approve it? – Moti Apr 05 '15 at 08:19
