prove that if sin(a/2) ≠ 0 then
cosa + cos2a +...+cos(n+1)a = (sin((n+1)a/2)*cos((n+1)a/2)/sin(a/2)
FInd this sum also in the case sin(a/2) = 0
Find a similar formula for sina + sin 2a +...+ sin(n+1)a
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Multiply it by . When you have sums like this - multiply by , r is ratio. Is signs alternate multiply the sum by .
Not sure what you mean.
"Is signs alternate multiply the sum by ." for example:
still not sure what you mean
Okay, what do you think I mean?
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