# Ellipse

- Ellipse (a two-dimensional figure) is a conic section or a stretched circle. It is a flat plane curve that when adding togeather any two distances from any point on the ellipse to each of the foci will always equal the same.
- Foci is a point used to define the conic section. F and G seperately are called "focus", both togeather are called "foci".
- The perimeter of an ellipse formula is an approximation that is about 5% of the true value as long as "a" is no more than 3 times longer than "b".
- The major axis is always the longest axis in an ellipse.
- The minor axis is always the shortest axis in an ellipse.

### Standard Ellipse Formula

\(\large{ \frac {x^2}{a^2} + \frac {y^2}{x^2} = 1 }\)

major axis horizontal : \(\large{ \; \frac { \left( x - h \right )^2 } { a^2 } + \frac { \left( y - k \right )^2 } { b^2 } = 1 }\)

major axis vertical : \(\large{ \; \frac { \left( x - h \right )^2 } { b^2 } + \frac { \left( y - k \right )^2 } { a^2 } = 1 }\)

Where:

\(\large{ x }\) = horizontal coordinate of a point on the ellipse

\(\large{ y }\) = vertical coordinate of a point on the ellipse

\(\large{ a }\) = length semi-major axis

\(\large{ b }\) = length semi-minor axis

\(\large{ h }\) and \(\large{ k }\) = center point of ellipse

### Area of an Ellipse formula

\(\large{ A = \pi \;a\; b }\)

Where:

\(\large{ A }\) = area

\(\large{ a }\) = length semi-major axis

\(\large{ b }\) = length semi-minor axis

\(\large{ \pi }\) = Pi

### Foci of an Ellipse formula

\(\large{ c^2 = a^2 - b^2 }\)

Where:

\(\large{ c }\) = length center to focus

\(\large{ a }\) = length semi-major axis

\(\large{ b }\) = length semi-minor axis

\(\large{ F }\) and \(\large{ G }\) = focus

### Perimeter of an Ellipse formula

This is an approximate perimeter of an ellipse formula. There is no easy way to calculate the ellipse perimeter with high accuracy.

\(\large{ p \approx 2\; \pi\; \sqrt { \frac{1}{2} \left(a^2 + b^2 \right) } }\)

Where:

\(\large{ p }\) = perimeter approximation

\(\large{ a }\) = length semi-major axis

\(\large{ b }\) = length semi-minor axis

\(\large{ \pi }\) = Pi

### Semi-major Axis Length of an Ellipse formula

\(\large{ a = \frac{A}{\pi \; b} }\)

Where:

\(\large{ a }\) = length semi-major axis

\(\large{ A }\) = area

\(\large{ b }\) = length semi-minor axis

\(\large{ \pi }\) = Pi

### Semi-minor Axis Length of an Ellipse formula

\(\large{ b = \frac{A}{\pi \; a} }\)

Where:

\(\large{ b }\) = length semi-minor axis

\(\large{ A }\) = area

\(\large{ a }\) = length semi-major axis

\(\large{ \pi }\) = Pi