Question

a+b+c=180,show that sina+sinb+sinc=4cosa/2cosb/2cosc/2

Answer 1

google is your friend.
You might want to start here:

https://socratic.org/questions/if-a-b-c-pi-then-prove-that-sina-sinb-sinc-4cos-a-2-cos-b-2-cos-c-2