设区域D由x=0,y=0,x+y=,x+y=1围成,若I1=[ln(x+y)]3dxdy,I2=(x+y)3dxdy,I3=sin3(x+y)dxdy,则( ).

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问题 设区域D由x=0,y=0,x+y=,x+y=1围成,若I1[ln(x+y)]3dxdy,I2(x+y)3dxdy,I3sin3(x+y)dxdy,则(      ).

选项 A、I1≥I2≥I3
B、I2≥I3≥I1
C、I1≤I2≤I3
D、I2≤I3≤I1

答案B

解析≤x+y≤1得[ln(x+y)]3≤0,于是I1[ln(x+y)]3dxdy≤0;
≤x+y≤1时,由(x+y)3≥sin3(x+y)≥0得I2≥I3≥0,
故I2≥I3≥I1,选(B).
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