- 3rd kind discontinuity - see continuity
- tan
- tangent line - see Derivatives - Theory - Applications - Tangent and normal lines and Derivatives - Methods Survey - Applications - Tangent and normal lines
- tanh
- Taylor polynomial and series
- telescopic series - see Series - Theory - Introduction - Summing up series and Series - Methods Survey - Summing up series - Summing up telescopic series
- testing convergence of improper integrals - see Integrals - Theory - Improper integrals - Convergence tests and Integrals - Methods Survey - Improper integrals
- testing convergence of sequences of functions - see Series - Methods Survey - Series of functions - Sequences of functions
- testing convergence of series of functions - see Series - Methods Survey - Series of functions - Series of functions
- testing convergence of series of numbers - see Series - Theory - Testing convergence and Series - Methods Survey - Testing convergence
- tests of convergence
- theorem
- total differential - see Derivatives - Theory - Introduction - Higher order derivative, total differential
- total differential in substitution - see Integrals - Theory - Methods of integration - Substitution, see also a note here
- transformation - see mapping
- transformation of a function - see Functions - Theory - Real functions - Operations and Functions - Methods Survey - Basic properties - Transformations
- transformations and Fourier series - see Series - Theory - Series of functions - Properties of Fourier series
- transitive law - see Extra - Sets and mappings - Important sets of numbers
- trichotomy law - see Extra - Sets and mappings - Important sets of numbers
- tricks
- trigonometric functions
- trigonometric polynomial - see Series - Theory - Series of functions - Fourier series
- trigonometric series - see Series - Theory - Series of functions - Fourier series
- type of expression (functions) - see Functions - Theory - Limit - Intuitive evaluation
- type of expression (sequences) - see Sequences - Theory - Limit - Intuitive evaluation and this note