【正文】
n10c o s70t a n220c o s20c o s2120s i n2310c o s70t a n2??????????????????????原式練習(xí) 5s in ( ) , ( 0 )4 1 3 4xx??? ? ? ?1. 已 知c o s 2c o s( )4xx??求 的值。1324xxxxx tan)2tantan1(c os2 2s i n ???2 si n c os si n 1 c os( 1 )2 c os c os si n1 c ossi n ( 1 ) t a nc ost a n t a n si nsi n 2