【正文】
2 , ,2 2 2 2 2t t t? ? ? ? ? ? ? ? ? ? :原式2 0 0 000 0 0 02 c o s 1 0 c o s 5 s in 5s in 1 0 ( )4 s in 1 0 c o s 1 0 s in 5 c o s 5? ? ?0 0 0000c o s 1 0 c o s 1 0 2 s in 2 02 c o s 1 02 s in 1 0 2 s in 1 0?? ? ?0 0 0 0 0 0 0 0c o s 1 0 2 s in ( 3 0 1 0 ) c o s 1 0 2 s in 3 0 c o s 1 0 2 c o s 3 0 s in 102 s in 1 0 2 s in 1 0? ? ? ??? 0 3cos30 2??