旋转体的体积=对{底面积π[√(x-1)]²×高dx(微元法)}求连续和(积分)
故
∫(1→4)π[√(x-1)]²dx
=∫(1→4)π(x-1)dx
=∫(1→4)(π/2)d(x-1)²
=(π/2)[(4-1)²-(1-1)²]
=9π/2