结束结束结束结束解?
例 4? 求函数 xy? 的导数?
解? ( 1 ) xxxy
( 2 ) xxxxxxx xx xxxxy 1)(?
( 3 ) xxxxxyy xx 2 11limlim 00
( 2 ) xxxxxxx xx xxxxy 1)(? ( 2 ) xxxxxxx xx xxxxy 1)(?
( 3 ) xxxxxyy xx 2 11limlim 0 ( 3) xxxxxyy xx 2 11limlim 00