Finding length segment of an ellipse

[highwhey]

Homework Statement

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.

Homework Equations

find L=f(x)

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.

 

[LCKurtz]

Homework Statement

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.

Homework Equations

find L=f(x)

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.

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.

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