题目内容
(请给出正确答案)
[主观题]
设函数z=f(u),u=x2+y2且f(u)二阶可导,则=()A.4f''(u)B.4xf''(u)C.4yf''(u)D.4xyf''(u)
设函数z=f(u),u=x2+y2且f(u)二阶可导,则=()
A.4f''(u)
B.4xf''(u)
C.4yf''(u)
D.4xyf''(u)
答案
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