`cosC+cosD`=
`(a) 2sin((C+D)/2)cos((C-D)/2)`
`2cos((C+D)/2)cos((C-D)/2)`
`(c) 2cos((C+D)/2)sin((C-D)/2)`
`(d)` none of these

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

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

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

The value of intsqrt(1+secx)dx is equal to (A) 2sin^-1(sqrt(2)sin(x/2))+c (B) 2cos^-1(sqrt(2)sin(x/2))+c (C) 2sin^-1(sqrt(2)cos(x/2))+c (D) none of these

In a quadrilateral if (sin (A + B)) / (2) (cos (AB)) / (2) + (sin (c + D)) / (2) + (sin (c + D)) / ( 2) (cos (cD)) / (2) = 2, then (cos A) / (2) (cos B) / (2) + (cos A) / (2) (cos c) / (2) + (cos A) / (2) (cos D) / (2) + (cos B) / (2) (cos C) / (2) + (cos B) / (2) (cos D) / (2) + (cos C) / (2) (cos D) / (2)

Show that: sin(B-C)cos(A-D)+sin(C-A)cos(B-D)+sin(A-B)cos(C-D)

Prove that: sin(B-C)cos(A-D)+sin(C-A)cos(B-D)+sin(A-B)cos(C-D)

(d)/(dx)(cos (x/2))= (A) (1)/(2)sin(x)/(2) , (B) -(1)/(2)cos(x)/(2) (C) -(1)/(2)sin(x)/(2) , (D) -sin(x)/(4)

In quadrilateral ABCD, if sin((A+B)/(2))cos((A-B)/(2))+sin((C+D)/(2))cos((C-D)/(2))=2 then find the value of sin(A)/(2)sin(B)/(2)sin(C)/(2)sin(D)/(2)