\left(\lim_{x \to c}{\frac{f_1(x)-f_1(c)-Df_1(c)(x-c)}{||x-c||}}, ...,\lim_{x \to c}{\frac{f_m(x)-f_m(c)-Df_m(c)(x-c)}{||x-c||}}\right)
= (0, ..., 0)