Question

(trig. prob.)
For all values of A,B,C , Prove that-

Answer 1

\[cosA+cosB+cosC+\cos(A+B+C)=4\cos \frac{A+B}{2}\cos \frac{B+C}{2}\cos \frac{A+C}{2}\]

Answer 2

you know 2cosa cosb identity ?

Answer 3

yes

Answer 4

@shubhamsrg

Answer 5

any progress you have made so far ?

Answer 6

i am not getting cos (B+C)/2 and cos (A+C)/2
instead i am getting cos (B+C) and cos (A+C)

Answer 7

leme see

Answer 8

maybe you should try to simplify RHS and convert it to LHS, seems easier to me that ways.