例如 y=x3, dy x=2 =3x2.dx x=2 =0.24 dx=0.02 dx=0.02 又如，y=arctanx, 1 +r2d dy=例如, , 3 y = x dy d 0.02 2 = = x x 2 = 3x dx d 0.02 2 = = x x = 0.24 y = arctan x , dy x x d 1 1 2 + = 又如