yellowhighlighterr
Active Member
I've gotten the first part of the question, but its the last bit that I stumble with. I followed the same steps to solve it but to no avail...
Any help??
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- Thread starter yellowhighlighterr
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I've gotten the first part of the question, but its the last bit that I stumble with. I followed the same steps to solve it but to no avail...
Any help??
scaryshark09
∞∆ who let 'em cook dis long ∆∞
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how do you do the first part?
Last edited:
There are of course other methods, some listed here: https://math.stackexchange.com/ques...-frac2-pi7-cos-frac4-pi7-cos-frac6-pi7-frac12
I suspect there is more to the question yellowhighlighterr didn't put there.
It is unlikely such question would be asked unscaffolded.
I suspect there is more to the question yellowhighlighterr didn't put there.
It is unlikely such question would be asked unscaffolded.
Last edited:
yellowhighlighterr
Active Member
aaaah ok. thanks m8
+\cos(\frac{3\pi}{7})+\cos(\frac{5\pi}{7})&=\textstyle-\cos(\pi-\frac{\pi}{7})-\cos(\pi-\frac{3\pi}{7})-\cos(\pi-\frac{5\pi}{7})\\&=\textstyle-\cos(\frac{6\pi}{7})-\cos(\frac{4\pi}{7})-\cos(\frac{2\pi}{7})\\&=\textstyle-(\cos(\frac{2\pi}{7})+\cos(\frac{4\pi}{7})+\cos(\frac{6\pi}{7}))\\&=\textstyle-(-\frac{1}{2})\\&=\textstyle\frac{1}{2}\end{aligned})