# CLASS-4CONSTRUCTION OF ANGLE WITH PROTRACTOR

CONSTRUCTION OF AN ANGLE WITH PROTRACTOR -

▪ The protractor is used for measuring angles. The unit for measuring angles is degree. The symbol for degree is ° written upside to the right of the number like  25°, 30°, 45°, 75°, 120°

To construct an angle using a protractor, follow these steps :-  1. Place the protractor on a flat surface with the base line of the protractor aligned with the base of the angle to be constructed.
2. Line up the center point of the protractor with the vertex (the point where the two sides of the angle meet).
3. Look for the zero-degree mark on the protractor and align it with one of the sides of the angle.
4. Read the degree measurement where the other side of the angle crosses the protractor scale. This is the degree measurement of the angle you want to construct.
5. Mark the angle using a pencil and ruler.
6. Draw a line through the vertex and the marked points to complete the angle.
7. Finally, label the angle with its degree measurement.

Note: If the degree measurement of the angle is greater than 180 degrees, then you will need to draw two lines instead of one. Here,  ∠ COB = 30°

▪    Align the baseline of the protractor with the line AB.

▪    The centre circle of the protractor at the vertex O.

1.  If the angle to be measured is in the left side, use the outer readings of the protractor and if the angle to be measured is in the right side, use the inner readings.

2. To reduce errors, align the baseline and vertex properly. If the angle to be measured is in the left side, use the outer readings of the protractor and if the angle to be measured is in the right side, use the inner readings.

EXAMPLE 1:-

STEPS TO CONSTRUCT AN ANGLE OF 60° PROCEDURE:

1.  Draw a ray YZ.

2.  Place the protractor in such a way that its centre is at the point Y and straight edge along YZ.

3.  Holding the protractor, observe along the scale till the 60 mark on the rim.

4.  On that mark put a dot and name it X.

5.  Remove the protractor and join Y to X. Thus, ∠ XYZ = 60°.  Arms: YX, YZ Vertex: Y

XYZ = 60°

This is an acute angle.

EXAMPLE. 2)  Construct an angle of 115° and label it. Arms: BA, BC Vertex: B

∠ ABC = 115°

This is an obtuse angle