Show that : `cos A+ cosB + cosC+ cos(A+B+C) = 4cos""(B+C)/(2)cos""(C+A)/(2)cos""(A+B)/(2)`.

If A + B + C + D = 2pi , prove that: cos A + cos B + cos C + cos D =-4"cos"(A+B)/(2)"cos"(A+C)/(2)"cos"(A+D)/(2)

If A+B+C+D=2pi , show that : cosA-cosB+cosC-cosD=4sin( (A+B)/(2)) sin( (A+D)/(2)) cos( (A+C)/(2)) .

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

sin A + sin B + sin C = 4cos ((A) / (2)) cos ((B) / (2)) cos ((C) / (2))

Theorem 4:sin A+sin B+sin C=4(cos A)/(2)(cos B)/(2)(cos C)/(2)

4R cos ((A) / (2)) cos ((B) / (2)) cos ((C) / (2)) =

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

If A+B+C=180^(@) then cos2A+cos2B+cos2C=1-4cos A cos B cos C 2.If A+B+C=0 then cos A+cos B+cos C=-1+4(cos A)/(2)(cos B)/(2)(cos C)/(2)

In Delta ABC, show that (1-cos A+cos B+cos C)/(1-cos C+cos A+cos B)=tan((A)/(2))cot((C)/(2))