# Volume of solid formed by revolution of one loop of Lemniscate of bernoulli

1. Sep 24, 2008

### raghavhv

Hello ppl. I have a problem in finding out the volume of solid formed by the revolution of one loop of lemniscate of bernoulli ( r²=a²cos2θ) about the initial line θ =0

Using the relevant forumula for the volume of the solid generated by the revolution of one loop of the polar curve about the initial line,

http://img357.imageshack.us/img357/4228/93696380jt5.jpg [Broken] ,

where V is the volume of the solid and π/4 and 0 are the upper and lower limits respectively.

In this problem ,

http://img88.imageshack.us/img88/6624/19344682ul0.jpg [Broken]

But i am not able to integrate further. I am kinda stuck here. What substitution should i take?Please help me.

Last edited by a moderator: May 3, 2017
2. Sep 24, 2008

### gabbagabbahey

Try using the following trig identity:

$$cos(2 \theta )=2cos^2( \theta )-1$$

And then use a substitution like $$u \equiv \sqrt{2} cos( \theta )$$

Last edited by a moderator: May 3, 2017