Question

Sin A - sin B - sin C=-4cos A 2 .sin B 2 .sin C 2​

Answer 1

sinA+sinB+sinC

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

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

=2cosC/2(cos(A-B)/2+cos(A+B)/2)

=4 cos A/2 cos B/2 cos C/2

= RHS