Cayley-Hamilton Theorem
## Definition / Concept
Every square matrix satisfies its own characteristic equation.
For a $$2\times2$$ matrix:
$$A^2-(\operatorname{tr}A)A+|A|I=O$$
where $$\operatorname{tr}A$$ is the trace of $$a$$.
## Usage
- Used to reduce higher powers of a matrix to lower powers.