updates
How many positive integers are factors of a given number?
I've been trying to find / generate a formula for the following problem: Given a number, how many positive integers are factors of this number. In pr...
Apr 21, 2026
Archive: Updates
updates
What is the concept behind this derangement formula?
In permutations and combinations, what is the concept behind this derangement formula? $$D_n = n!\left(1-\dfrac{1}{1!}+\dfrac{1}{2!}-\dfrac{1}{3!}+...+(-1...
Apr 21, 2026
updates
Properties of functions of normal random variables
$\newcommand{\Cov}{\operatorname{Cov}}$As an extension of this question (covariance of normal distribution), I'd like to give a specific example, and...
Apr 21, 2026
![can you use pythagoras on a non right angled triangle [closed]](https://news.conceivablytech.com/uploads/can-you-use-pythagoras-on-a-non-right-angled-triangle-closed_720.jpg)
updates
can you use pythagoras on a non right angled triangle [closed]
Sorry I'm a bit confuse, are you allow to use Pythagoras in a non right angled triangle?
Apr 21, 2026
updates
Robinson arithmetic and its incompleteness
Wikipedia in Italian has a sketch-of-proof that Robinson arithmetic is not complete, since commutativity of addition is undecidable. The sketch of proof c...
Apr 21, 2026
updates
Computing Hessian in Python using finite differences
I am computing the Hessian of a scalar field, and tried using numdifftools. This seems to work, but was quite slow so I wrote my own approach using finite...
Apr 21, 2026
updates
Null Space and Orthogonal Complement
I'm having trouble understanding in a mathematical sense the reason why: (1) $$Null(A) = [R(A^{T})]^\perp $$ (2) $$Null(A^T) = [R(A)]^\perp$$ What I&...
Apr 21, 2026
updates
SR Unit Conversion Speed
What is 72,000 km/hour in Système Relativistique (SR) units? I am getting 1/14490 or 1/14490th of the speed of light.
Apr 21, 2026
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Intuition on the sum of first (n-1) numbers is equal to the number of ways of picking 2 items out of n.
While going through an equation today i realized that sum of first (n-1) numbers is [n*(n-1)/2] which is equal to combinations of two items out of n i.e [...
Apr 21, 2026
updates
Construct a 98% confidence interval for the population proportion of defective toys.
A toy company would like to estimate the proportions of toys produced by their younger workers. In a random sample of 300 toys, they found that 75 were de...
Apr 21, 2026
