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

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

If A+B+C = pi , prove that : cosA+cosB + cosC = 1+4sinA/2sinB/2sinC/2 .

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=pi , prove that : cos2A+cos2B+cos2C=-1-4cosA cosB cosC

If A+B+C=(3pi)/(2) , then show that cos 2A+cos 2B+cos 2C=1-4 sin A sin B sin C .

If A + B + C = pi , then show that sin (A + B + C)/( 2) = sin(A / 2) * cos "" (B + C)/( 2) + sin "" (B + C)/( 2) * cos "" (A) / (2)

If A + B + C = pi then prove that cos A + cos B + cos C = 1 + 4 sin(A/2) .sin(B/2).sin(C/2)

let a=cosA+cosB-cos(A+B) and b=4sin(A/2)sin(B/2)cos((A+B)/2) Then a-b is

Prove that (cosA-cosB)^2+(sin A-sin B)^2=4sin^2((A-B)/2)