if Sin A +Sin B =root 3 ( cos B -cos A) then , Sin 3A + sin 3B is ?

Divide the first eqn by 2 and obtain the general solution. From iot, obtain the 2 principle solutions of the equations one of which will be null and void(you can check it by putting it in the eqn which will then contradict itself.) Put the valid solution in Sin 3A+Sin 3B to obtain the solution.