设 x=o(t), y=m(,二阶可导, d y o(ty(t)-o"(ty(t) de '(t) dx 2 3 h≤9(t)y"(1)-yy(a p2(t)+v"2(t)2 上页, ( ), ( ), 设 二阶可导    = = y t x t   . [ ( ) ( )] ( ) ( ) ( ) ( ) 2 3 2 2 t t t t t t k        +    −    = , ( ) ( ) t t dx dy      = . ( ) ( ) ( ) ( ) ( ) 2 3 2 t t t t t dx d y         −   =