Prove that `4cos(2pi)/7dotcospi/7-1=2cos(2pi)/7dot`

Prove that cos(2pi)/(15)cos(4pi)/(15)cos(8pi)/(15)cos(14pi)/(15)=1/(16)

Prove that: cos^4pi/8+cos^4(3pi)/8+cos^4(5pi)/8+cos^4(7pi)/8=3/2

Find the value of cos(2pi)/7+cos(4pi)/7+cos(6pi)/7

Prove that 2 cos""(pi)/(13)cos""(9pi)/(13)+cos""(3pi)/(13)+cos""(5pi)/(13)=0

Find the value of 2cos^3(pi/7)-cos^2(pi/7)-cos(pi/7)

Prove that cos^(2)""pi/8+cos^(2) ""(3pi)/(8)+cos^(2)""(5pi)/(8)+cos^(2)""(7pi)/(8)=2

Show that "cos"(pi)/(15)"cos"(2pi)/(15)"cos"(3pi)/(15)"cos"(4pi)/(15)"cos"(5pi)/(15)"cos"(6pi)/(15)"cos"(7pi)/(15)=(1)/(128) .

In triangle A B C , prove that sin(A/2)+sin(B/2)+sin(C/2)lt=3/2dot Hence, deduce that cos((pi+A)/4)cos((pi+B)/4)cos((pi+C)/4)lt=1/8

Show that 16cos((2pi)/(15))cos((4pi)/(15))cos((8pi)/(15))cos((16pi)/(15))=1