Mathematics
Area and perimeter of any 2D shape
Simplify an aspect ratio and resize without distortion
A fast, free online calculator
Binary, hex and bitwise arithmetic
Area, circumference, radius, sector & arc
Arithmetic, polar form, powers and roots
Differentiate any function, exactly
Raise any number to any power
Factor polynomials and find their roots
Add, subtract, multiply and divide fractions
Greatest common divisor and least common multiple
Antiderivatives and definite integrals
Evaluate limits, one-sided or at infinity
Solve 2×2 and 3×3 systems with working
log, ln, log₂ and any custom base
Long division with full worked steps
Determinant, inverse, eigenvalues and more
Mean, median, mode, spread, quartiles & outliers
Mod, GCD, modular inverse and power
Square root, cube root, any nth root + surds
Write any number in words
How far a measurement is from the true value, as a percentage
Add, multiply, divide and evaluate polynomials
Is it prime? Plus full factorisation
Solve a : b = c : x for the missing value
Find a missing side of a right triangle
Simplify any ratio to its lowest terms
Round to places, sig figs, or nearest 5/10/100
Trig, logs, powers, roots and more
Nth term and sum of an arithmetic or geometric sequence
Solve any triangle from 3 measurements
sin, cos, tan, their reciprocals and inverses
Dot, cross, magnitude, angle and projection
Volume and surface area of any solid
A4 is the answer to an equation, and US Letter is not the answer to anything
Two constraints — a ratio of √2 and an area of one square metre — have exactly one solution, and that solution...
NA
20 Sep
The Fluid Blowup Proofs Are Machine-Checkable. The Competing Claim Was a Press Call.
Buckmaster and Alpöge published three preprints with Lean formalisations anyone can run. The results are for f...
NA
9 Sep
Why two websites give you different life path numbers
Numerology has two standard ways of doing the arithmetic, and for about one birthday in eight they disagree. T...
AM
31 Aug
The pattern behind the order of the 64 hexagrams
The I Ching's numbered sequence has a strict rule running through it that almost no introduction mentions — an...
EV
31 Aug
Why Your Best Performers Get Worse
A thousand simulated pages whose true conversion rates never change. Selected on one period's numbers, the top...
NA
24 Aug
What Happens When You Test Twenty Metrics
A dashboard rarely shows one number. Simulated with nothing real to find, examining twenty metrics produced at...
NA
24 Aug
How Big Does an A/B Test Need to Be?
Sample size is usually decided by how long someone will wait. Simulated across a grid, a genuine one-point lif...
NA
23 Aug
What Happens When You Check an A/B Test Early
Twenty thousand simulated experiments with no real difference in them. Read once at the end, 4.9% came back si...
NA
23 Aug
Why "Random" Is Almost Never Random — and What a Fairness Test Cannot See
We fed the same rejection-sampling helper a cryptographic source and a 1960s textbook generator, 600,000 draws...
KE
2 Aug
Mean, Median, Mode: The Average Is a Choice, Not a Fact
Three different numbers are all correctly called "the average", and which one gets published changes what a re...
NA
26 Jul
A High R² Does Not Mean the Model Is Right
Anscombe printed one regression summary for four data sets in 1973 and said the features that matter are "invi...
NA
26 Jul
Standard Deviation vs Standard Error: Two Numbers, Two Questions
Mean ± 4.36 and mean ± 0.97 are not two ways of saying the same thing. Altman and Bland assigned each to a dif...
NA
26 Jul
What a 95% Confidence Interval Actually Means
Nearly everyone reads a confidence interval as "there is a 95% probability the true value is in here" — includ...
NA
26 Jul
Option Greeks, Explained: Delta, Gamma, Theta and Vega Without the Jargon
An option's price moves for four reasons, and the Greeks are the dials that tell you how much it responds to e...
SA
24 Jul