设f(x)连续,且f(0)=1,令F(t)=f(x2+y2dxdy(t≥0),求F’’(0).

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问题 设f(x)连续,且f(0)=1,令F(t)=f(x2+y2dxdy(t≥0),求F’’(0).

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答案由F(t)=∫0dθ∫0trf(r2)dr=2π∫0trf(r2)dr=π∫2t2f(u)du, 得F’(t)=2πtf(t2),F’(0)=0, [*]=2πf(0)=2π.

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