• 2022-07-26
    设[img=49x25]1803577bfb31342.png[/img]是二元可微函数, [img=88x42]1803577c0441258.png[/img],则 [img=103x47]1803577c0ce559b.png[/img]
    A: [img=108x42]1803577c1544164.png[/img]
    B: 0
    C: [img=108x42]1803577c1d387c0.png[/img]
    D: [img=108x42]1803577c25e9773.png[/img]