Prove `(i)cos C+cosD=2cos((C+D)/2)cos((C-D)/2)` (ii)`cosC-cosD=2sin((C+D)/2)sin((D-C)/2)`

Prove (i)sin C+sin D=2(sin(C+D))/(2)(cos(C-D))/(2)(ii)sin C-sin D=2(sin(C-D))/(2)(cos(C+D))/(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=180^(@), then prove that cos^(2)(A)/(2)+cos^(2)(B)/(2)+cos^(2)(C)/(2)=2(1+sin(A)/(2)sin(B)/(2)sin(C)/(2))

cos(A-D)sin(B-C)+cos(B-D)sin(C-A)+cos(C-D)sin(A-B)=0

Prove in any triangle ABC that (i) a(cos B+cos C)=2(b+c) "sin"^(2)(A)/(2) (ii) a(cos C- cosB)= 2(b-c )"cos"^(2)(A)/(2)

ln a quadrilateral ABCD if sin((A+B)/2)cos((A-B)/2)+sin((C+D)/2)cos((C-D)/2)=2, then sin(A/2)sin(B/2)sin(C/2)sin(D/2) has the value equal to (a)1/8 (b)1/4 (c)1/(2sqrt2) (d)1/2

If A+B+C=180^0 , prove that : cos^2( A/2) + cos^2( B/2) + cos^2(C/2) = 2+2 sin(A/2) sin( B/2) sin( C/2)

In any triangle ABC, prove that (i) (a-b)/( c)=("sin"(A-B)/(2))/("cos"( C)/(2)) (ii) (b-c)/(a)=("sin"(B-C)/(2))/("cos"(A)/(2))

If A+B-C=3pi, t h e n sin A+ sin B-sin C is equal to- a.4sin(A/2)sin(B/2)cos(C/2) b. -4sin(A/2)sin(B/2)cos(C/2) c. 4cos(A/2)cos(B/2)cos(C/2) d. -4cos(A/2)cos(B/2)cos(C/2)

If A,B,C are the angles of a triangle then prove that cos A+cos B-cos C=-1+4cos((A)/(2))cos((B)/(2))sin((C)/(2))