- Trigonometric equations
- sin q = 0 Þ q = np, n Î Z
- tan q = 0 Þ q = np, n Î Z
- If a is some constant angle, then
- cos q = cos a Þ q = 2np ± a, n Î Z
- tan q = tan a Þ q = np + a, n Î Z- If a is some constant angle, then
- tan2 q = tan2 a Þ q = n p ± a , n Î Z
Relation between sides and angles of a triangle
- If ABC is a triangle with sides a = BC, b = CA, c = AB, then

- a = b cos C + c cos B
- b = c cos A + a cos C (Projection formula)
- c = a cos B + b cos A



Definitions of inverse trigonometric functions




Some properties of inverse trigonometric functions
In the principle value branches, the following formulae holds:
- cos-1 (cos x) = x
- tan-1 (tan x) = x- cos-1 (cot x) = x
- sec-1 (secx) = x- cosec-1 (cosecx) = x
- sin-1 (-x) = -sin-1 x
- cos-1 (-x) = p - cos-1 x
- tan-1 (-x) = -tan-1 x- cot-1 (-x) = p -cot-1 x
- sec-1(-x) = p - sec-1 x- cosec-1 (-x) = -cosec-1 x










