If `A+B+C=pi,` then `cos ^(2) ""(A)/(2) + cos ^(2) ""(B)/(2) - cos ^(2) ""(C )/(2)`

If A+B+C =pi, then cos ^(2) A+ cos ^(2)B + cos^(2) C is equal to

If A+B+C=pi then prove that cos^2 (A/2)+cos^2 (B/2)-cos^2 (C/2)=2cos(A/2)cos(B/2)sin(C/2)

If A+B+C=pi , then cos 2A+cos 2B+cos 2C=

cos ""(2pi)/( 15) cos ""(4pi)/(15) cos ""(8pi)/(15) cos ""(16pi)/(15)=

2cosx-cos3x-cos5x= ............... A) 16 cos ^(3) x sin ^(2) x B) 16 sin^(2) x cos ^(2) x C) 4 cos ^(2) x sin ^(2) x D) 4 sin ^(2) x cos ^(2)x

If A+B+C=pi , prove that cos 2A +cos 2B +cos 2C=-1-4cos A cos Bcos C.

cos 15^(@) =............. A) sqrt((1+cos 30^(@))/(2)) B) sqrt((1-cos 30^(@))/(2)) C) pm sqrt((1+cos 30^(@))/(2)) D) pm sqrt((1- cos30^(@))/(2))

sin^2 17. 5^(@)+sin^2 72. 5^(@) is equal to............ A) cos ^(2) 90^(@) B) tan ^(2) 45^(@) C) cos ^(2) 30^(@) D) sin ^(2) 45^(@)

In DeltaABC,(a-b)^(2)cos^(2).(C)/(2)+(a+b)^(2)sin^(2).(C)/(2) =