*Complete trigonometry introduction 

and problems solve of book.

 *Trigonometry is the science of relationships between the sides and angles of a right-angled triangle.

*Trigonometric Ratios: Ratios of sides of right triangle are called trigonometric ratios.

*Consider triangle ABC right-angled at B. These ratios are always defined with respect to acute angle ‘A’ or angle ‘C.

*If one of the trigonometric ratios of an acute angle is known, the remaining trigonometric ratios of an angle can be easily determined.

*How to identify sides: Identify the angle with respect to which the t-ratios have to be calculated. Sides are always labelled with respect to the ‘θ’ being considered.

therefore the abbreviated notations are:

sine A is sin A
cosine A is cos A
tangent A is tan A
cosecant A is cosec A
secant A is sec A
cotangent A is cot A

* An equation involving trigonometric ratio of angle(s) is called a trigonometric identity, if it is true for all values of the angles involved.