Look at the adjoining protractor in which a straight line AOB is divided into 180 small parts. Each part is a degree or 1°.

The most common unit of measurement of an angle is the degree. The
system of measuring angles in degrees, minutes, and seconds is called **Degree Measure** or **Sexagesimal System**.

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Degrees are divided by placing the vertex of the angle at the
centre of a circle of some fixed radius. Then the circumference of the circle
is divided into 360 equal parts, each part is called a degree.

In trigonometry, an angle is defined in different ways. In the adjoining figure, let O be a fixed point and OX a fixed-line. OP is a line which initially coincides OX and revolves about O. The amount of rotation of OP about O with respect to OX is called an angle between OX and OP and written as ∠POX. Initially, when OP coincides OX, there is no rotation and the angle formed is zero.

Hence, the amount of rotation of a revolving line about a fixed
point with respect to the initial line is called an **angle**.

If OP rotates about O in an anticlockwise direction, the angle formed by this is positive and if OP rotates about O in a clockwise direction, the angle formed by this is negative.

If the line OP has made a complete rotation and again 60°, then the angle made by OP is 360° + 60° = 420°. Similarly, if OP has made two complete rotation and again 60° then the angle made by OP is 2×360° + 60° = 780° and so on.

One-fourth of a complete rotation is called a right angle. In
sexagesimal system, a right angle is divided into 90 equal parts and each part
is called degree. Further, each degree is subdivided into 60 equal parts called
minutes and each minute is subdivided into 60 equal parts called seconds.

We denote the degrees, minutes and seconds by the symbol (°), (Ê¹)
and (Êº) respectively.

Thus, we have,

1 right angle = 90 degrees (90°)

1 degree = 60 minutes (60Ê¹)

1 minute = 60 seconds (60Êº)

So, 45° 50Ê¹ 55Êº means 45 degrees, 50 minutes, and 55 seconds.

We have,

1 right angle = 90°

1° = 60Ê¹

1Ê¹ = 60Êº

**Worked Out Examples**

**Example 1:** Convert into sexagesimal seconds 45° 35Ê¹ 25Êº.

**Solution:** Here,

45° 35Ê¹ 25Êº = (45×60×60 + 35×60 + 25)Êº

= (162000 + 2100
+ 25)Êº

= 164125Êº Ans.

**Example 2:** Reduce 44° 30Ê¹ 45Êº to the degrees.

**Example 3:** Express 60.1532° into degrees, minutes, and seconds.

**Solution:** Here,

60.1532° = 60° (0.1532×60)Ê¹

= 60° 9.192Ê¹

= 60° 9Ê¹
(0.192×60)Êº

= 60° 9Ê¹ 11.52Êº
Ans.

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