- trigonometric polynomials of best approximation
- trigonometric ratio
- trigonometric representation of complex number
- trigonometric series
- trigonometric substitution
- trigonometric sum method
- trigonometric sum with prime numbers
- trigonometry
- trihedral angle
- trihedral angle
- trihedral axes of space curve
- trilateration
- trinomial equation
- trioctahedron
- TRI-operator algebras
- tripartite graph
- triple contact circles
- triple integral
- triplesolution theorem
- triplicate ratio circle
- trirectangular spherical triangle
- trirectangular tetrahedron
- trisectrix
- trisectrix of an angle
- trivial absolute value