Formulae cosC±cosD, sinC±sinD

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

In any quadrilateral ABCD, show that: cosA cosB-cosC cosD="sin"A "sin"B-"sin"C "sin"D.

If A+C=2B, then (cosC-cosA)/(sinA-sinC)=

If A+B+C=pi , prove that : cosA sinB sinC +cosB sinC sinA+cosC sinA sinB=1+cosA cosB cosC .

In a triangle ABC,k right angled at B, if tan A = (1)/(sqrt3). Find the value of cos A.cosC-sinA.sinC.

If A+B+C=pi , prove that : sinA cosB cosC +sinB cosC cosA + sinC cosA cosB = sinA sinB sinC .

If ABCD is a cyclic quadrilateral, then find the value of sinA + sinB -sinC - sinD

Let A,B,C,D be the angles of a quadrilateral . If they are concyc lic , then the value of cosA+cosB+cosC+cosD is

In a triangle Delta ABC, angleB = 90^(@) and tanA = sqrt""3 then what is the value of sinA.cosC + cosA.sinC?