Aide-mémoire de maths du métier

Right triangle

Hypotenuse: c = √(a² + b²). A missing leg: a = √(c² − b²). The 3-4-5 (and its multiples, 6-8-10, 9-12-15) squares a corner without a square.

Area & volume

Rectangle: length × width. Triangle: ½ × base × height. Circle: π × r². Box volume: length × width × height. Cylinder: π × r² × length.

Percentages & ratios

Percent of a number: (percent ÷ 100) × number. Percent change: (new − old) ÷ old × 100. A ratio a : b scales by multiplying both sides by the same factor.

Conversions

All of this is public arithmetic and geometry — nothing on this sheet is code-book data. π ≈ 3.1416.