2 (根号3) [ sin (B +π/3) +sin B ]
=2 (根号3) *2 sin [ (B +π/3 +B) /2 ] cos [ (B +π/3 -B) /2 ]
=4 (根号3) *sin (B +π/6) cos (π/6) +3
=6 sin (B +π/6) +3.
= = = = = = = = =
和差化积：
sin A +sin B = 2 sin [ (A+B) /2 ] cos [ (A-B) /2 ].