由微分的定义及上述定理可知若f(x)在x处可导 则f(x)在x处可微,且=f(x0)Ax 当M关0时1m=m4 40dx0f(x)4 →!~(4x→>0)→4=+0(4y) 4y-dy 4y-f'(roar m In Ax→>0 x→0 4 f(xo =0由微分的定义及上述定理可知 若f (x)在x0处可导 则f (x)在x0处可微，且dy = f (x0 )x 当f (x0 )  0时 1 ( ) lim lim 0 0 0 =  = → → f x x y dy y x x       y ~ dy (x → 0)  y = dy + o(y) y y f x x y y dy x x        ( ) lim lim 0 0 0 −  = − → →            = − → x y f x x    ( ) lim 1 0 0 = 0