In triangle ABC, prove that `cos(A/2)+cos (B/2)+cos(C/2)`= `4cos (pi-A)/4cos(pi-B)/4cos(pi-C)/4`

If A+B+C=180 , prove that: sinA+sinB+sinC=4cos(A/2)cos(B/2)cos(C/2)

Prove that: cos(pi/7)cos(2pi/7)cos(4pi/7)=-1/8,

In a triangle ABC, prove that: cos^4A+cos^4B+cos^4C= 3/2 + 2 cosA cosB cosC+ 1/2 cos 2A cos2B cos2C

In a triangle ABC, prove that (a) cos(A + B) + cos C = 0 (b) tan( (A+B)/2)= cot(C/ 2)

Prove that: cos(pi/5)cos((2pi)/5)cos((4pi)/5)cos((8pi)/5)=(-1)/16

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

If A+B+C=pi , prove that : cosA + cosB-cosC=4cos(A/2) cos(B/2) sin(C/2) -1

Prove that 4cos((2pi)/7).cos(pi/7)-1=2cos((2pi)/7) .

Prove that: cos(pi/4+x)+cos(pi/4-x)=sqrt(2)\ cos x

Prove that: cos(pi/7)cos((2pi)/7)cos((4pi)/7)=-1/8