Using a protractor
Make a triangle such as the one below. Then, using a protractor measure each of its angles.
In our case,
∠a = 70°
∠b = 45°
∠c = 65°
Now, add all these angles.
∠a + ∠b + ∠c = 70° + 45° + 65° = 180°
We notice that the angle sum of the above triangle is 180°.
Try making a couple of triangles, measure their angles and record their angle sums. You will observe that in every case, the angle sum of a triangle is 180°.
Using the hands-on method
Make a triangle as below. Then cut it into 3 pieces and arrange the pieces next to each other.
Upon putting the pieces together you will notice that the 3 corners join together to form the sum of angles along a straight line which is 180°.
The angle sum or sum of angles of a triangle is 180°.