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Jonask Group TitleBest ResponseYou've already chosen the best response.0
\[\huge{\cos \frac{\pi}{7}}\cos \frac{2\pi}{7}+\cos \frac{3\pi}{7}=\frac{1}{2}\]
 one year ago

Jonask Group TitleBest ResponseYou've already chosen the best response.0
so far i managed to write \[\cos \frac{ \pi }{ 7 }2\cos^2\frac{ \pi }{ 7 }+1+\cos \frac{ 2\pi }{ 7 }\cos \frac{ \pi }{ 7 }\sin \frac{ 2\pi }{ 7 }\sin \frac{ \pi }{ 7 }\] \[\cos \frac{ \pi }{ 7 }2\cos ^2\frac{ \pi }{ 7 }+1+2\cos^3\frac{ \pi }{ 7 }\cos \frac{ \pi }{ 7 }2\cos \frac{ \pi }{ 7 }+2\cos^3\frac{ \pi }{ 7 }\] \[4\cos^3\frac{ \pi }{ 7 }2\cos^2\frac{ \pi }{ 7 }2\cos\frac{\pi}{7}+1\]
 one year ago

Jonask Group TitleBest ResponseYou've already chosen the best response.0
without using a calculator
 one year ago

Jonask Group TitleBest ResponseYou've already chosen the best response.0
guys i have the solution but it is so superficial i'll put it just now
 one year ago

Jonask Group TitleBest ResponseYou've already chosen the best response.0
no idea about S
 one year ago

Jonask Group TitleBest ResponseYou've already chosen the best response.0
is that the bookmark symbol
 one year ago

sauravshakya Group TitleBest ResponseYou've already chosen the best response.2
cos(pi/7) cos(2pi/7)+ cos(3pi/7) cos(pi/7)+cos(3pi/7)+cos(5pi/7) {2sin(pi/7)cos(pi/7) + 2 sin(pi/7) cos(3pi/7) + 2 sin(pi/7) cos(5pi/7)}/2 sin(pi/7)
 one year ago

shubhamsrg Group TitleBest ResponseYou've already chosen the best response.0
That is just a comment, which will enable me to receive notifications whenever it gets discussed * is just a symbol, yes, bookmark symbol
 one year ago

Jonask Group TitleBest ResponseYou've already chosen the best response.0
are you saying cos 2 pi/7=cos 5 pi/7
 one year ago

Jonask Group TitleBest ResponseYou've already chosen the best response.0
cos 2a=cos 5a
 one year ago

sauravshakya Group TitleBest ResponseYou've already chosen the best response.2
cos(5pi/7) =cos(pi 2pi/7) = cos(2pi/7)
 one year ago

Jonask Group TitleBest ResponseYou've already chosen the best response.0
k very clear
 one year ago

sauravshakya Group TitleBest ResponseYou've already chosen the best response.2
It is because cos(pia)=cosa
 one year ago

sauravshakya Group TitleBest ResponseYou've already chosen the best response.2
Now, u need to use 2 sinA cosB = sin(A+B)  sin(AB)
 one year ago

sauravshakya Group TitleBest ResponseYou've already chosen the best response.2
Sorry, The correct formula is 2 sinA cosB =sin(A+B) + sin(AB) =sin(A+B)  sin(BA)
 one year ago

sauravshakya Group TitleBest ResponseYou've already chosen the best response.2
=cos(pi/7) cos(2pi/7)+ cos(3pi/7) =cos(pi/7)+cos(3pi/7)+cos(5pi/7) ={2sin(pi/7)cos(pi/7) + 2 sin(pi/7) cos(3pi/7) + 2 sin(pi/7) cos(5pi/7)}/2 sin(pi/7) ={sin(2pi/7) sin(0) +sin(4pi/7) sin(2pi/7) +sin(6pi/7) sin(4pi/7)}/2sin(pi/7) ={sin(6pi/7)}/2sin(pi/7) ={sin(pi/7)}/2sin(pi/7) =1/2
 one year ago

sauravshakya Group TitleBest ResponseYou've already chosen the best response.2
sin(6pi/7) =sin(pi pi/7) =sin(pi/7)
 one year ago

Jonask Group TitleBest ResponseYou've already chosen the best response.0
okay that makes so much sense i guess elementary steps we skipped
 one year ago

Jonask Group TitleBest ResponseYou've already chosen the best response.0
so we just had to play with\[\pi \pm \frac{\pi}{7}\]
 one year ago

sauravshakya Group TitleBest ResponseYou've already chosen the best response.2
yep... and one formula
 one year ago
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