Thread: polar form of complex number sign problem

just got this worksheet back, and on this particular problem i'm told i messed up the negative/postive signs. I probably did...but i can't figure out how.

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12cis 210

12(cos210 + i sin 210)

(this next part is where i messed up the signs)

12(sqrt3 /2 + i 1/2)

answer: 6sqrt3 + 6i
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but doesn't cos 210deg = -sqrt3/-2? making it an overall positive?

and same for the sin 210deg?

cos 210 = - cos 30 = -sqrt(3)/2. Think of the cosine wave.