风6*灯i山 解令x=tant,dk=sec2d,x=l,=Tx=V3,t 4 一3 z-j原arnH -sec2tdt 3 dsint π sin't sin2t 1 3 √2 23 sint π 3 4 13 13 例 6 求 3 1 2 2 1 1 dx x x +  解 令 2 tan , sec , 1,t= ; 3,t= 4 3 x t dx tdt x x   = = = = 3 3 2 1 2 2 2 2 4 1 1 sec 1 tan 1 tan dx tdt x x t t  =  + +   3 3 2 2 4 4 cos sin sin sin t d t dt t t   = =     1 3 sin 4 t   = − 2 3 2 3 = −