MHB Do Pi and Geometric Shapes Coexist?

AI Thread Summary
The discussion explores the presence of pi in various geometric shapes, noting that pi is integral to the area of ellipses and circles but not directly applicable to polygons like squares. It emphasizes that while angles in polygons involve pi, the coordinates and sides are typically algebraic numbers, which do not inherently include pi unless mapped to a circle. The complexity of calculating the circumference of an ellipse leads to the use of elliptic integrals, hinting at hidden pi values. Additionally, the conversation touches on the relationship between pi and physics formulas, which often involve full turns, suggesting a deeper connection between geometry and physical concepts. Overall, the discussion highlights the nuanced role of pi across different geometric contexts.
highmath
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(1) Is there a pi in ellipse entity?Why not or yes?
(2) Is there a pi in polygons entities (e.g square)? not or yes?
(3) If there is pi in some geometries and other not - What is the reason to that?
(4) How cloud I know that are no hidden formula of pi in a square figure that the expression in formula, his value is: 0 in addition and 1 in multiplicatoin and etc
 
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I really don't understand what you mean by this. "$\pi$" is a number. What do you mean by a number "in" in a geometric figure? If you mean formulas for circumference, area, etc. Then it is true that the area of an ellipse, with semi-axes of lengths a and b is $\pi ab$, very similar to the formula for the area of a circle. On the other hand, while the circumference of a circle is simply $2\pi r$, there is no simple formula for the area of an ellipse.
 
highmath said:
(1) Is there a pi in ellipse entity?Why not or yes?
(2) Is there a pi in polygons entities (e.g square)? not or yes?
(3) If there is pi in some geometries and other not - What is the reason to that?
(4) How cloud I know that are no hidden formula of pi in a square figure that the expression in formula, his value is: 0 in addition and 1 in multiplicatoin and etc
I'll add a note here:
The Greeks, at least, defined [math]\pi[/math] as the circumference of a circle divided by its diameter. So [math]\pi[/math] does come up in a lot of geometric figures. But if you are trying to find some deeper reasoning to it you aren't going to find it. It's just a handy definition.

-Dan
 
highmath said:
(1) Is there a pi in ellipse entity?Why not or yes?
(2) Is there a pi in polygons entities (e.g square)? not or yes?
(3) If there is pi in some geometries and other not - What is the reason to that?
(4) How cloud I know that are no hidden formula of pi in a square figure that the expression in formula, his value is: 0 in addition and 1 in multiplicatoin and etc

We can roughly divide geometry in angles and coordinates.
We see $\pi$ in the domain of the angles and not in the domain of the coordinates.
In a simple right angle on the unit circle we have the simplest possible coordinates with $0$ and $1$.
Its angle is $\smash{\frac \pi 2}$.
Its hypotenuse is $\sqrt 2$, which is an algebraic number and not transcendental like $\pi$.
So $\pi$ comes along whenever an angle or turn is involved.
To find the area of a circle, we integrate over the angle so that we see $\pi$ back in the result.

An ellipse is a circle scaled in one direction by a factor, which scales its area by the same factor.
So yes, there is $\pi$ in the area of an ellipse.
The circumference of an ellipse is so complicated that an elliptic integral function was invented to describe it.
Still, there is probably a $\pi$ hidden in there somewhere.

The coordinates of a polygon and its sides are typically algebraic numbers.
Its angles contain $\pi$, but $\pi$ only shows up if we map the polygon into the domain of a circle, since that is how angles have been defined. If we would identify angles by their coordinate ratios (slopes) there would be no $\pi$.

Through projective geometry a circle is transformed, or rather is equivalent to an ellipse, a parabola, and a hyperbola. These are the so called conic sections.
We already saw $\pi$ in the area of an ellipse.
A parabola and a hyperbola don't have an area though as they are unbounded. If we bound a parabola with a line at an algebraic coordinate, we don't see $\pi$, but we see an algebraic number. A hyperbola bounded by a line gives an area that contains $e$ instead of $\pi$.
The arc length of a parabola also contains $e$, while the arc length of a hyperbola is too complicated to tell.

We see $\pi$ a lot in physics formulas as well, and usually as $2\pi$ or $4\pi^2$. What these formulas have in common is that they deal with a full turn. As we know, the arc length of a full turn is $2\pi r$. All those physics formulas would be simplified if we used $\tau$ for a full turn instead of $2\pi$.
 
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