# some one prove me wrong please or just agree?

someone prove this wrong

I agree with all of you that there is no easy way to find the circumference of an ellipse but all an oval is is a stretched circle that is easy to make round again. finding the circumference of a circle is easy right. To change the oval to a circle X+Y*Pi were X and Y are the two radius "the shortest and longest lines from the center of the oval" by adding X and Y and you get the diameter of a circle with the same circumference as the oval so to get the circumference you just multiply by 3.14

Update:

one or the other prove me wrong prove me right or both I dont care

Update 2:

JB I am undoing the stretch kind of like taking a little bit off the high side and adding it to the smaller off the two till they are equel think propertion I could just say X+Y/2*3.14*2 more or less bring the radios into play but by doing that division X+Y/2 I then have to mulitply at the end of the equation by 2 like a circle 2*pi*radius same thing but here both sides of the circle are already even

Update 3:

all i need is the two radius to find a diameter its the right diameter for the calculation Im not saying I can draw the outling of the opisit if I have a circle whith a 1in radius I make two 1 in radius at 90degree change one to .75 and the other to .50 its an oval but no i cant outling the shape

Update 4:

David U are overlooking that pi is a constant think of an astroid in an elipticle orbit when it aproctes earth is when it speeds up and because of that is is not trully elipticle

Update 5:

david if I took a squar and spun it around would it not outling a circle if i closed my eyes and type eventualy I would spell a word so is it not probable that is I took a rectanle and spun it around evuntualy it would outline an oval

Relevance
• JB
Lv 7

The reason your argument is wrong is that the length of little pieces of your ellipse (or of your circle) change by different scale factors depending on the direction in which they point. If they are nearly perpendicular to the stretch direction their length changes hardly at all, but if they are nearly parallel to the stretch direction their length changes by nearly the full scale factor. For your argument to work, the scale factor would have to apply to all the same.

Interestingly, your argument works fine for area. The area of an ellipse is pi ab, where a, b are semi major and semi minor axes. When a=b then it is a circle and you get pi r^2, where r=a=b is the radius.

The reason the argument works for area, is that if you subdivide the area into many little squares, each square is affected identically by the stretch, and it is in the direction of one side of the square, so the area of the ellipse is just the scale factor times the area of the circle.

• David
Lv 7

no, that is incorrect.

the curvature of an ellipse isn't constant, so the ratio of the circumference to the sum of the major and minor axis lengths is not pi.

imagine you are driving a car whose speed depends on how tightly you're turning. if you're on a circular track, you're always going the same speed, but on an elliptical track, you speed up and slow down. now distance = speed times elapsed time, so measuring a circle is easy, you can just measure the elapsed time, but measuring an ellipse is MUCH more complicated, because your speed keeps changing.

the trouble with your idea, in general, is that by "stretching" the circle to an ellipse, you have to include an adjustment for the stretching itself, and there is no SIMPLE formula for doing this.

Lets try it out.