设函数f(x,y)连续,则∫12dx∫x2f(x,y)dy+∫12dy∫y4-yf(x,y)dx=( ).

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问题 设函数f(x,y)连续,则∫12dx∫x2f(x,y)dy+∫12dy∫y4-yf(x,y)dx=(     ).

选项 A、∫12dx∫14-xf(x,y)dy.
B、∫12dx∫x4-xf(x,y)dy
C、∫12dx∫14-yf(x,y)dy.
D、∫12dx∫yyf(x,y)dy

答案C

解析12dx∫x2f(x,y)dy+∫12dy∫y4-yf(x,y)dx的积分区域为两部分(如图4—8):D1={(x,y)|1≤x≤2,x≤y≤2};D2={(x,y)|1≤y≤2,y≤x≤4一y},将其写成一个积分区域为D={(x,y)|1≤y≤2,1≤x≤4一y}.故二重积分可以表示为∫12dy∫14-yf(x,y)dx,故答案为C.
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