# Proof by induction help

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#1
I was wondering if anybody could help me with this proof by induction question. Prove that

(1/2) + cos(x) + cos(2x) + ... + cos(nx) = [sin(n + (1/2))x]/2sin(x/2)

Thanks!
Last edited by pontifexmaximus; 1 month ago
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1 month ago
#2
As ever:

What have you tried so far?
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1 month ago
#3
(Original post by pontifexmaximus)
I was wondering if anybody could help me with this proof by induction question. Prove that

(1/2) + cos(x) + cos(2x) + ... + cos(nx) = [sin(n + (1/2))x]/2sin(x/2)

Thanks!
Do you understand the principle of proof by induction?

What is the base case? Can you prove it?

What is the inductive step? How might you prove it using standard trig formulae?
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