Question

1. If A,B,C are angles of a triangle prove that

cos A+cosB + cos C=1+4 sinA/2× sinB/2 ×sinC/2​

Answer 1

Step-by-step explanation:

Use the following identity:

Here is how. You know that

A + B = 180 - C

(A + B)/2 = 90 -C/2

c/2 = 90 - (A + B)/2

cos ( C/2) = cos ( 90 - (A + B)/2) = cos ( (A + B)/2 - 90) = sin ( (A + B)/2 )

where the last step used the identity given above, and the penultimate step used the fact that the cosine is an even function [ cos (a) = cos (-a) ].

Hope it's help UH.......:)

xXitzMeAngelXx