Formulas
- Area of a circle
- Arithmetic dynamics
- Arithmetic progression
- Array processing
- Arrow's impossibility theorem
- Arzelà–Ascoli theorem
- Askey–Wilson polynomials
- Asset turnover
- Assured clear distance ahead
- Astronomical coordinate systems
- Astronomical seeing
- Asymptote
- Asymptotic analysis
- Asymptotic equipartition property
- Asymptotic theory (statistics)