阁阳.则类喻=与数 dx 狼兴 第点-a安 ewh-fo0 dt( ) ( ( )) 2 2 f t dx d dx dy dx d dx d y = = dx dt f t dt d = ( ( )) 记 ( ) ( ) ( ) f t t t dx dy =   =   ， 则 y对 x的二阶导 数 ( ) 1 ( ) t f t  =   dt dx f t dt d 1 = ( ( ))