Question

To verify the properties of sides and angles of a triangle using geometrical instruments.?

Answer 1

The sum of two smaller sides of a triangle is always greater then third big side

Answer 2

) the sum of the angles in a triangle is 180°.

Take any triangle ABC. Construct XY through B and parallel to AC. Using the properties of parallel
lines angle A = angle XBA and angle C = angle CBY. Hence the angle sum of the triangle is angle A + angle ABC + angle C = angle XBA + angle ABC + angle CBY = 180° = angles on a straight line.

You must remember the basic angle facts such as the sum of the angles on a straight line is 180°, and the properties of alternate and corresponding angles.



(b) the exterior angle of a triangle is equal to the sum of the interior opposite angles.

Take any triangle ABC. Construct a line through C, parallel to AB.

angle p = angle b (corresponding angles)
angle s = angle a (alternate angles)

Therefore angle p + angle s = angle a + angle b

but angle r = angle a + angle b

Therefore angle p + angle s = angle r