戈 df(x) 即 lim △y im f(x0+△x)-∫(x0) y|x=xo△r→0△x△x→>0 △ 其它形式f(x1)=lim f(x0+h)-f(x0) h f(xo)=lim f(x)-f(x0) x→x x-d Economic- mathematics 21-7 Wednesday, February 24, 2021Economic-mathematics 21 - 7 Wednesday, February 24, 2021 . ( ) ( ) ( ) lim 0 0 0 0 h f x h f x f x h + −  = → 其它形式 . ( ) ( ) ( ) lim 0 0 0 0 x x f x f x f x x x − −  = → x f x x f x x y y x x x x  +  − =    =  →  → = ( ) ( ) lim lim 0 0 0 0 0 , ( ) ( ) , x x0 x x0 x x0 dx d f x dx dy f x = = =  或 即