Trig Pythagorean Identities
For angle θ at which the functions are defined:
(1) cos2θ + sin2θ = 1
(2) 1 + tan2θ = sec2θ
(3) 1 + cot2θ = csc2θ
(2) 1 + tan2θ = sec2θ
(3) 1 + cot2θ = csc2θ
Dividing both
sides of the first equation by cos2θ results in
the second equation. Similarly, dividing both sides of the
first equation by sin2θ results in the third
equation.
Other Trigonometric Identities:
- Reciprocal Identities
- Even-Odd Identitites
- Cofunction Identities
- Half-Angle Identities
- Double-Angle Identities
- Sum and Difference Identities
- Sum to Product Identities
- Product to Sum Identities