Intereting Posts

Are there any examples of non-computable real numbers?
$f: \mathbf{R} \rightarrow \mathbf{R}$ monotone increasing $\Rightarrow$ $f$ is measurable
What is the resistance between two points a knights move away on a infinite grid of 1-ohm resistors
If $\phi(n)$ divides $n-1$, prove that $n$ is a product of distinct prime numbers
$|G|=12$ and no elements of order $2$ in $Z(G)$
Proof on showing if F(x,y,z)=0 then product of partial derivatives (evaluated at an assigned coordinate) is -1
Inversion of matrices is a diffeomorphism.
Primitive recursive function which isn't $\Delta_0$
How many digits of accuracy will an answer have?
Revisted$_2$: Are doubling and squaring well-defined on $\mathbb{R}/\mathbb{Z}$?
How do I evaluate the integral $\int_0^{\infty}\frac{x^5\sin(x)}{(1+x^2)^3}dx$?
Normal subgroup of prime order is characteristic
If $B\times \{0\}$ is a Borel set in the plane, then $B$ is a Borel set in $\mathbb{R}$.
Given distinct maximal ideals $M_1,…,M_n$, is $M_1\cdots M_n$ radical?
Minimality in the case of partial derivatives and Sobolev spaces?

What is the minimal number of points $N$ to uniquely define the semi-major axis $a$, the semi-minor axis $b$ and the rotation angle $\omega$ of an ellipse whose the center is known/fixed (this is related to ellipse fitting procedures).

In other words, if we consider that the center is known/fixed, on this image what is the minimal number of blue points I need to compute $a$, $b$ and $\omega$ in a unique way ?

EDIT: and what is the number of points needed when the center of the ellipse is not known ?

- Did Euclid prove that $\pi$ is constant?
- Numbers of circles around a circle
- Trying to understand why circle area is not $2 \pi r^2$
- Recurrent points and rotation number
- Parametric Equation of a Circle in 3D Space?
- How many sides does a circle have?

- Eccentricity of an ellipse
- Prove that the directrix is tangent to the circles that are drawn on a focal chord of a parabola as diameter.
- Finding the largest triangle inscribed in the unit circle
- Classifying complex conics up to isomorphism as quotient rings of $\mathbb{C}$
- Good books on conic section.
- Definite integral: $\displaystyle\int^{4}_0 (16-x^2)^{\frac{3}{2}} dx$
- What are the subsets of the unit circle that can be the points in which a power series is convergent?
- Compute center, axes and rotation from equation of ellipse
- Parametric Equation of a Circle in 3D Space?
- Centre of the circle

The equation of an ellipse is given by

$$ ax^2+by^2+cxy+dx+ey+f = 0 $$

where $(a,b,c,d,e,f)\in\mathbb{P}^5(\mathbb{R})$, hence you need $5$ points to recover the coefficients, if you do not know where the center is. Otherwise, $3$ points (such that no two of them are symmetric with respect to the center) are enough, since their mirror images with respect to the center of the ellipse still lie on the ellipse, so having $3$ points and the center is like having $6$ points on the ellipse. Obviously, having two points and the center is not enough, since there are many concentric ellipses that pass through the same two points.

- On Conjugacy Classes of Alternating Group $A_n$
- Multiplicative property of the GCD
- Partitioning the edges of $K_n$ into $\lfloor \frac n6 \rfloor$ planar subgraphs
- On Tarski-Knaster theorem
- Area enclosed between the curves $y=x^2$ and $y=60-7x$
- What is linearity?
- Find all of the homomorphisms $ \varphi: \mathbb{Z}_{15} \to \mathbb{Z}_{6} $.
- Continuation of smooth functions on the bounded domain
- Returning Paths on Cubic Graphs Without Backtracking
- Interior of a convex set is convex
- Special case of the Hodge decomposition theorem
- Why should I go on and differentiate this?
- $K$ consecutive heads with a biased coin?
- An analytic function with a simple pole
- How to solve simultaneous equations using Newton-Raphson's method?