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JonaskBest 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

JonaskBest 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

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

JonaskBest 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

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

sauravshakyaBest 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

shubhamsrgBest 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

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

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

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

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

sauravshakyaBest 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

sauravshakyaBest 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

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

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

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

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