Question

please say the answer fast

Answer 1

Taking LHS:

=Sin^2 A/2+sin^2 B/2+sin^2 C/2

=1-cos^2 A/2 +sin^2 B/2+sin^2 C/2

=1-(cos(A+B)/2 cos(A-B)/2) + sin^2 C/2

= 1-(cos(pi-C)/2 cos(A-B)/2)+sin^2C/2

= 1+sin C/2(sin C/2 -cos(A-B)/2)

=1+sin C/2(sin(pi –(A+B)/2 -cos(A-B)/2)

=1+sin C/2(cos (A+B)/2-cos(A-B)/2)

= 1+sin C/2(-2sinA/2 sinB/2)= 1-2sinA/2 sin B/2 sin C/2  = RHS [hence proved].