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losang
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Why does the area of an ellipse have a closed form while the perimeter does not? Obviously if the area is finite so is the boundary so it seems the perimeter should be calculable in a closed form.
Well, it just doesn't.losang said:Why does the area of an ellipse have a closed form while the perimeter does not?
Wrong implication. You can perfectly well have regions with finite areas, yet infinite boundaries.Obviously if the area is finite so is the boundary
Why should "closed form" have anything to do with finiteness?so it seems the perimeter should be calculable in a closed form.
marcusl said:The perimeter is
[tex]P=4aE(\pi/2,e)[/tex]
where a is the length of the semi-major axis, e is eccentricity and E is the complete elliptic integral of the second kind, a well-known, tabulated function.
losang said:We could lay a string on the perimeter and in the limit get the exact length by measuring the string. In other words for a circle there is a closed form but as the axis vary wrt one another there is no cloded form. Why?
losang said:show me.
Sure enough:losang said:show me.
Since the radius varies strongly as a function of polar angle theta, it is not surprising that the perimeter expression is complicated. The real question is why the area expression is simple.losang said:Why does the area of an ellipse have a closed form while the perimeter does not? Obviously if the area is finite so is the boundary so it seems the perimeter should be calculable in a closed form.
The formula for calculating the perimeter of an ellipse is P = 2π√((a^2+b^2)/2), where a and b are the semi-major and semi-minor axes of the ellipse, respectively.
The perimeter of an ellipse is not a constant value like that of a circle. It varies depending on the size and shape of the ellipse. Unlike a circle, which has a constant radius, an ellipse has two different radii (semi-major and semi-minor) which contribute to its perimeter formula.
Yes, the perimeter of an ellipse can be greater than the perimeter of a circle with the same area. This is because the perimeter of an ellipse is affected by both the length and width, whereas the perimeter of a circle is only affected by the radius.
If only the area of an ellipse is given, you can use the formula P = 2√(πA), where A is the area of the ellipse. This formula can be derived from the formula for calculating the area of an ellipse, A = πab, where a and b are the semi-major and semi-minor axes.
Yes, there are many real-life applications for calculating the perimeter of an ellipse. For example, it is used in architecture and engineering for designing curved structures, and in astronomy for calculating the orbits of planets and other celestial bodies. It also has applications in fields such as physics, optics, and computer graphics.