# Finding length segment of an ellipse

1. Mar 27, 2013

### highwhey

1. The problem statement, all variables and given/known data

i'm having trouble with these solid of revolution problems because a lot of them require you to find "length of the segment" before evaluating the problem. example:
a solid lies between planes perpendicular to x=-5 and x=5. the cross section in the xy plane is the ellipse ((x2)/25)+((y2)/36)=1.

2. Relevant equations
find L=f(x)

3. The attempt at a solution
does that mean i mean i have to make the given equation a function of x? because when i attempt that, it does not turn out to be correct.
according to the example this is the correct result, L=(12/5)√(25-x2) how can i arrive at that result?

thank you in advance. by the way, i am posting from my ipad so if the format of the question is not correct, i apologize.

2. Mar 27, 2013

### LCKurtz

I have no idea what you are asking. What does "find L = f(x)" mean? Or "find a length segment"? Volume or surface area might make sense.

 Maybe you are asking for the radius of revolution about the x axis? In which case you would solve for y.