问题
填空题
设f(u)是连续函数，平面区域D=(x，y)|x≥0，y≥0，1≤x2+y2≤4，则
=______．
答案
参考答案：
解析： 令x=rcosθ，y=rsinθ，在极坐标系(r，θ)中D={(r，θ)| 0≤θ≤
，1≤r≤2}，
=r，dσ=rdrdθ，故
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设f(u)是连续函数，平面区域D=(x，y)|x≥0，y≥0，1≤x2+y2≤4，则
=______．
参考答案：
解析： 令x=rcosθ，y=rsinθ，在极坐标系(r，θ)中D={(r，θ)| 0≤θ≤
，1≤r≤2}，
=r，dσ=rdrdθ，故
What does the speaker mean to Jane a. The speaker will not join the party until half past ten. b. If the speaker can finish his work before half past ten, s/he will join the party. c. If the speaker does not arrive at the party until half past ten, s/he will not join the party. d. The speaker is not able to join the party because he will not be available until half past ten.