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March 22nd, 2019, 08:39 AM  #1 
Member Joined: Feb 2018 From: Iran Posts: 38 Thanks: 3  Finding volume of solid formation using disck method
find the volume of the solid figure generated by rotating the area of the region bounded y=1/x the x axis x=1 and x=3 about y_axis How to solve this question using ring methode? I've added my way of solving the question but I am not sure if its true if it's not can you please say where I did wrong? 
March 22nd, 2019, 08:50 AM  #2 
Math Team Joined: Jul 2011 From: Texas Posts: 2,887 Thanks: 1506 
two integrals are required ... $\displaystyle V = \pi \int_0^{1/3} 3^2  1^2 \, dy + \pi \int_{1/3}^1 \left(\dfrac{1}{y}\right)^2  1^2 \, dy$ one integral using cylindrical shells ... $\displaystyle V = 2\pi \int_1^3 x\left(\dfrac{1}{x}\right) \, dx$ 

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disck, finding, formation, method, solid, volume 
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