ðɪs ɹɪzˈʌlt kæn biː əbtˈeɪnd mˈʌtʃ mˈoːɹ sˈɪmpli baɪ nˈoʊɾɪsɪŋ ðætðə fˈʌŋkʃən hɐz ɡɹˈeɪdiənt , sˌoʊ baɪ ðə ɡɹˈeɪdiənt θˈiəɹəm:
This result can be obtained much more simply by noticing that the function  has gradient , so by the Gradient Theorem: