Thread: Complex Exponential Form

I was asked this question can someone please help I do not know where to start
Find the sum to n terms:
a) cosΘ + cos3Θ + cos5Θ + ...

the answer should be (-cos((2n+1)Θ)+cos((2n-1)Θ))/(2(1 - cos2Θ))

I don't know hoe to go about answering this question.
Please Help

Originally Posted by sthato

I was asked this question can someone please help I do not know where to start
Find the sum to n terms:
a) cosΘ + cos3Θ + cos5Θ + ...

the answer should be (-cos((2n+1)Θ)+cos((2n-1)Θ))/(2(1 - cos2Θ))

I don't know hoe to go about answering this question.
Please Help

Start by observing that you have a finite geometric series.

CB

I have noticed that, but I still don't know how to go about answering the question.