### Mathematics Class XI

Unit-I: Sets and Functions
Chapter 1: Sets
Unit-II: Algebra
Chapter 5: Binomial Theorem
Chapter 6: Sequence and Series
Unit-III: Coordinate Geometry
Chapter 1: Straight Lines
Chapter 2: Conic Sections
Unit-IV: Calculus
Unit-V: Mathematical Reasoning
Unit-VI: Statistics and Probability
Chapter 1: Statistics
Chapter 2: Probability

If a rotation from the initial side to terminal side is of a revolution, the angle is said to have a measure of one degree, written as .

A degree is divided in 60 minutes and  a minute is divided in 60 seconds

Some angles are shown below (In degree)

Angle subtended at the centre by an arc of length in a unit cirlce (circle of radius is said to be a measure of  radian.

The circumference of a circle of radius . Thus, one complete revolution of the initial sides subtends an angle of  radian.

In a circle of radius , an arc of length or subtends an angle whose measure is radian, an arc of length will subtend an angle whose measure is .

Thus, is a circle of radius , an arc length length subtends an angle radian at centre, we have

Some angles whose measures are in radian shown below:

Or

Also,

Notational Convention

Example:

We know

Example:

Find the radius of the circle in which a central angle of intercepts an arc of length

Solution:

Here,

Hence,

Example: