【正文】
oss i ns i n 2222 ??)1c os2)(1c os2(21c osc oss i ns i n 222222 ????? ??????原式21c osc osc osc oss i ns i n 222222 ????? ??????21c oss i nc oss i ns i n 22222 ???? ?????21c oss i n 22 ??? ??解法 1: 解法 2: ??????2c os2c os21)2c os1)(2c os1(41)2c os1)(2c os1(41???????原式???? 2c os2c os21)2c os2c os1(21 ???21? ?????? 2c os2c os21c os)s i n1(s i ns i n 2222 ????原式????? 2c os2c os212c oss i nc os 22 ???)2c os21(s