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

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

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 : cosA- cosB - cosC = 1-4sinA//2cosB//2cosC//2 .

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

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 prove that sin(B+2C)+sin(C+2A)+sin(A+2B)=4sin((B-C)/(2))sin((C-A)/(2))sin((A-B)/(2))

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

If A+B+C=2pi , prove that : cos^2B+cos^2C-sin^2A-2cosA cosB cosC=0 .