https://www.teachoo.com/question/13711/Cos20%C2%B0cos40%C2%B0cos60%C2%B0cos80%C2%B0=1-16/
https://www.teachoo.com/question/13711/Cos20%C2%B0cos40%C2%B0cos60%C2%B0cos80%C2%B0=1-16/
Find coeff. Of three consecutive terms in expansion of(1+a)n are in ratio 6:33:110.find n