关于高一数学,麻烦解答一下,谢谢

左边=sin[(B+C)+(B-C)] - sin[(B+C)-(B-C)]
=sin(B+C)cos(B-C) + cos(B+C)sin(B-C) - sin(B+C)cos(B-C) + cos(B+C)sin(B-C)
=2sin(B-C)cos(B+C)
=右边
即可证明~