OBJECTIVE

To verify that the sum of the angles of a triangle is 180°

MATERIALS REQUIRED

White chart paper

Geometry box

Scissors

Adhesive

Drawing sheet

PREREQUSITE KNOWLEDGE

Knowledge of straight angle

PROCEDURE

Take a cardboard of suitable size and  paste a white chart paper on it.

Draw a Δ ABC of suitable lengths on the drawing sheet and paste it on the cardboard.

                                                                     Image1

 Cut out the angles respectively equal to ∠A , ∠B and ∠C from a drawing sheet,.by using tracing paper

Image 2

                                                                               Image 3

                                                                      Image 4

Draw a line on the cardboard and arrange  the three  cut outs of the angles (∠A, ∠B and ∠C) on the line at a point O 

                                                                       Image 5

OBSERVATION

When all the three cut outs of the angles A, B, C placed adjacent to each other at a point, then it forms a line forming a straight angle, i.e. 180°.

Thus  it is proved that the sum of the three angles of a triangle is 180°.

Therefore  ∠A + ∠B + ∠C =180°

(Measure &write)

Measure of ∠A = ………… ,
Measure of ∠B = ………… ,
Measure of ∠C = ………… ,
Hence, sum (∠A + ∠B + ∠C) = ………… .

CONCLUSION

The sum of angles of a triangle is 180°