是个环形物体.
上限是1,下限是0
围成图形的曲线是y=lnx x = e^y以及x = e
体积V = π∫(0到1) [(e)² - (e^y)²] dy
= π∫(0到1) [e² - e^(2y)] dy
= π*[e²y - (1/2)e^(2y)],(0到1)
= π*[e² - (1/2)e² + (1/2)]
= (π/2)(1+e²)