【正文】
( c o ss i n( c o s xxxx ???2( s in c o s )xx??同角公式的應(yīng)用:證明 ? P25 13( 2) ???? 2222 s i ntans i ntan ???分析: ?? 22 s i nt a n ??證明:左邊 ??? 222s i nc oss i n ??????2222c osc oss i ns i n ?????222c os)c os1(s i n ?????222c oss ins in ????24c o ssin??? 22 s i nt a n ??右邊 ??? 22 s inc oss in