é¢ç§¯S=â«lnxdx(ä¸éeï¼ä¸é1)=xlnx-â«xd(lnx)=xlnx-â«x*(1/x)dx=xlnx-x代å
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S=e*lne-e-1*ln1+1=1
æ²çº¿x=g(y)å´ç»yè½´æ转çæ转ä½ä½ç§¯V=Ïâ«[g(y)]^2dy
y=lnx,x=e^y
V=Ïâ«(e^y)^2dy(ä¸élne,ä¸éln1)
=Ïâ«e^(2y)dy
=Ï*e^(2y)/2代å
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V=(Ï/2)*(e^2-1)
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