1. Jan 9, 2005

2. Jan 9, 2005

### arildno

Are you thinking of the perimeter of an ellipse?

As it happens, the formula is some nasty infinite series, if I'm not mistaken.

3. Jan 9, 2005

### Register

Sorry, I don't know what an ellipse is. I mean an oval with a radius of 20CM horizontally, and 7CM vertically.

I know that the formula to find it's area is:
20 X 7 X 3.14

I know there is a way to find it's perimeter. :p

4. Jan 9, 2005

### dextercioby

It is.It is called COMPLETE ELLIPTIC INTEGRAL OF THE FIRST KIND OF ANDRE MARIE LEGENDRE.
Do you want the formula,the series exapansion??

Daniel.

5. Jan 9, 2005

### Register

Yes, please give me the formula. ^_^

6. Jan 9, 2005

### dextercioby

There you go,for an ellipse of semiaxis "a" and "b" it reads
$$I_{ellipse}(a,b)=:4\int_{0}^{+\frac{\pi}{2}} \sqrt{a^{2}\sin^{2}\phi+b^{2}\cos^{2}\phi} d\phi$$

Daniel.

7. Jan 9, 2005

### Register

Thank you so much. You really helped a lot. ^_^

8. Jan 9, 2005

### dextercioby

You're welcome... I just hope u know you can't solve that integral exactly,doncha??I'm hoping you won't be spending your whole day trying to find the antiderivative and applying the Leibniz-Newton formula...
This integral is tabulated in many engineering books...

Daniel.

9. Jan 9, 2005

### Alex

Not to be rude, but, I find it that hard to believe considering that you didn't know what an ellipse was.

10. Jan 9, 2005

### rachmaninoff

Just wondering, is an oval actually an ellipse at all? Since an oval is the shape of an egg, and an egg only has one axis of symmetry (I mean a chicken egg). It's longer on one end, and rounder on the other.

11. Jan 10, 2005

### master_coda

You're right, an oval isn't an ellipse. I've never actually seen a precise mathematical definition of an oval (i.e. I don't know what the general equation of an oval is) but it would certainly not be the same as that of an ellipse.

However in this case I suspect that Register is actually talking about an ellipse and just doesn't know the correct name for it. The area equation given as an example is after all the equation for the area of an ellipse.

12. Jan 10, 2005