二重积分练习题答案

13、I=∫∫(x+ydxdy，D:x2+y2≤1D解：yD1I=4∫∫(x+ydxdyD10x=4∫π208dθ∫r(cosθ+sinθ⋅rdr=03114、设f(u为可微函数，f(0=0，求极限1lim3∫∫ft→0+πtx2+y2≤t2(x2+y2dσ高等数学——Copyright©2012bySamw.Allrightsreserved.2t⋅f(t=lim解：原式=tlim3+2→0t→0+πt3t2f(t−f(02=lim=f′(0+t3t→030162π∫r⋅f(rdrt