第1个回答 2017-04-25
作变换x=rcosu,y=rsinu,则所求体积
V=2∫<0,2π>du∫<0,a>rdr∫<0,√[a^2-r^2(cosu)^2]>dz
=2∫<0,2π>du∫<0,a>r√[a^2-r^2(cosu)^2]dr
=∫<0,2π>du/(cosu)^2*(-2/3){[a^2-a^2(cosu)^2]^(3/2)-a^3}
=(2/3)a^3∫<0,2π>[1-|sinu|^3]du/(cosu)^2
=(2/3)a^3{∫<0,π>[1-(sinu)^3]du/(cosu)^2+∫<π,2π>[1+(sinu)^3]du/(cosu)^2}
=(2/3)a^3{∫<0,π>[1+sinu+(sinu)^2]du/(1+sinu)+∫<π,2π>[1-sinu+(sinu)^2]du/(1-sinu)}
=(2/3)a^3{<0,π>[1/(1+sinu)+sinu]du+∫<π,2π>[1/(1-sinu)-sinu]du}
=(2/3)a^3[2+2+2+2]
=16a^3/3.