cos C + cos D =

If A+B+C+D=360^(@) , the prove that cos 2A + cos 2B + cos 2C + cos 2D =4 cos (A+B) cos (A+C) cos (A+D)

Prove that : cos C +cosD = 2 cos frac (C+D)(2) cos frac (C-D) (2) .

If A+ B + C = pi, then cos^(2) A + cos ^(2) B + cos ^(2) C is equal to : A) 1 - cos A cos B cos C B) 1 - 2 cos A cos B cos C C) 2 cos A cos B cos C D) 1 + cos A cos B cos C

If ABCD is a cyclic quadrilateral, then the value of cosA-cosB+cosC-cosD is............... A) 0 B) 1 C) 2(cos B- cos D) D) 2 (cos A- cos C)

If A+B+C=(3pi)/2 . Then cos 2A +cos 2B+cos2C is equal to ................. A) 1-4 cos A cos B cos C B) 4 sin A sin B sin C C) 1+2 cos A cos B cos C D) 1-4 sin A sin B sin C

(cos(A+B))/(cos(A-B))+(cos(C-D))/(cos(C+D))=0rArr cot A cot B cot C cot D=

Assertion (A) : Suppose that alpha- beta is not an odd multiple of (pi)/(2) , m in R-{0,1) and (sin (alpha+beta))/(cos (alpha-beta))=(1-m)/(1+m) then Tan ((pi)/(4)-alpha)=m cot ((pi)/(4)- beta) Reason (R) : for all C,D, & R cos c+cos D= 2 cos ((C+D)/(2)) cos((C-D)/(2)) cos-cosD=-2sin ((C+d)/(2))sin ((C-D)/(2))

For all, x in[0,(pi)/(2)] ,the minimum value of cos(cos x) A) 0 B) cos1 C) -cos1 D) 1

If : A+B+C=pi, "then" : sin 2A + sin 2 B - sin 2 C= A) 4 sin A * cos B * cos C B) 4 sin B * sin C * cos A C) 4 sin C * cos A * cos B D) 4 sin A * sin B * sin C