Trigonometry is a branch of mathematics which concerned with the measurement of sides, angles and their relation to a triangle. The relationship between the three sides of a triangle is simply known as Pythagoras theorem. This note has information about Pythagoras Theorem.

The ratios which are generally used to calculate the unknown lengths and angles in a right triangle is called trigonometric ratios. Trigonometric Expressions are the expressions in which variables are written under the signs of trigonometric functions. This note has information about trigonometric ratios, its operations, trigonometric expressions and reciprocals relations.

The triangle which consists three sides and three angles with six elements is known as right angled triangle. If three elements are given, one of which must be the side and remaining others elements can be calculated which is known as solution of right angle triangle.

The angle which is above the horizontal line and the condition from which the angle is formed by the line of sight with the horizontal line is called angle of elevation. The angle which is below the horizontal line and the condition from which the angle is formed with the horizontal line is called angle of depression.