Trigonometric Identities and Formulas
There are three systems of measuring Angles-
1. Circular System
- Unit of Measurement is radian.
- 180 degree = π radians
2. Sexagesimal System (English System)
- Right angle is divided into 90 equal parts called degree.
- Unit of Measurement is degree.
- Each degree is divided into 60 equal parts called minute. (1 degree = 60’)
- Each minute divided into 60 equal parts called seconds (1 minute = 60’’)
3. Centesimal or French System
- Right angle is divided into 100 equal parts.
- Unit of measurement is grades.
- Each grade is divided into 100 equal parts called minute, and minutes into seconds.
- cos (90 – θ) = sinθ
- tan (90 – θ) = cotθ
- cosec (90 – θ) = secθ
- sec (90 – θ) = cosecθ
- cot (90 – θ) = tanθ
Some Basic Formulas and Identities
- sin2θ + cos2θ = 1
- 1 + tan2θ = sec2θ
- 1 + cot2θ = cosec2θ