The number cis 75 + cis 83 + cis91 +...+ cis 147 is expressed in the form r cis(theta), where 0 <= theta < 360.

Find theta in degrees.

I need help.

6 answers

one way:

cos 75 + cos 83 + .....cos 147 = a

sin 75 + sin 83 + .... sin 147 = b

tan theta = b/a

r = sqrt (a^2+b^2)
I don't understand?
calculate a above.
calculate b above.

theta= arctan (b/a)
How do I calculate a and b?
I got 291 degrees. is that correct?
nvm its 111
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