# Math & Geometry

> Number theory, modular, geometry.

Canonical: https://learn.significanthobbies.com/curriculum/concepts/math-geometry

Number theory, modular, geometry.

- Difficulty: core
- Tracks: DSA & Implementation

## Mental model

Interviews use math sparingly: gcd/lcm, modular arithmetic, primes, combinatorics, and basic geometry (cross product, line intersection). Recognize the shape of the problem — the formula is a quick lookup away.



## Primary sources

- [Computational geometry (Wikipedia)](https://en.wikipedia.org/wiki/Computational_geometry) (doc)

## Practice

### GCD and modulo arithmetic

gcd(48,18)? What is (7^10) mod 13 via repeated squaring?

**Expected evidence:** gcd=6; 7^10 mod 13 = 4.

## Review prompts

- What does the sign of the 2D cross product tell you, and which problems does that single test solve?


## Prerequisites

- None assigned.

## Related concepts

- None assigned.

## Learning paths

- [DSA Practice](https://learn.significanthobbies.com/curriculum/roadmaps/dsa-practice)