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设D是平面有界闭区域,f(x,y)在D上连续,证明:若f(x,y)在D上非负,且 则在D上f(x,y)=0.
设D是平面有界闭区域,f(x,y)在D上连续,证明:若f(x,y)在D上非负,且 则在D上f(x,y)=0.
设D是平面有界闭区域,f(x,y)在D上连续,证明:
若f(x,y)在D上非负,且则在D上f(x,y)=0.
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设D是平面有界闭区域,f(x,y)在D上连续,证明:
若f(x,y)在D上非负,且则在D上f(x,y)=0.
设f(x,y)在闭区域D={(x,y)|x2+y2≤y,x≥0}上连续,且
求f(x.y).
设平面薄片所占的闭区域D由螺线p=2θ上一段弧(0≤θ≤)与直线
所围成,它的面密度为u(x,y)=x2+y2.求这薄片的质量.