Prove that in a quadrilateral ABCD, `cosA+cosB+cosC+cosD-4cos((A+B)/2)cos((A+C)/2)cos((A+D)/2)=0`

Prove that in a triangle ABC, bc cos A + ca cos B +ab cos C= 1/2(a^2+b^2+c^2)

In any quadrilateral ABCD,prove that sin(A+B)+sin(C+D)=0

Choose the correct option In a triangle ABC, sin((A+B)/2) is equal to a) cos(B-C)/2 b) cos(C-A)/2 c) cos(A/2) d) cos (C/2)

Show that in a triangle ABC, (b^2-c^2)/(cosB+cosC)+(c^2-a^2)/(cosC+cosA)+(a^2-b^2)/(cosA+cosB)=0

If ABCD be a cyclic quadrilateral,-prove that cos A + cos B + cos C + cos D = 0

Prove that (sin A+sin 2A)/(1+cos A +cos 2A)=tan A

Prove that (sin A+sin B)/(cos A+cos B)=tan((A+B)/2)

If A,B,C are the interior angles of ABC, then prove that cos((A+B)/2)=sin(C/2) .

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

In a ∆ ABC prove that cos ((A+B)/2) = sin (c/2) .