Q6 of 97 Page 205

Find the measure of each exterior angle of an equilateral triangle.

From the figure, we have

∠AOD is the exterior angle

∴ ∠AOD + ∠AOB = 180^o

60^o + ∠AOB = 180^o

∠AOB = 180^o – 60^o

∠AOB = 120^o

Hence, the measure of each of the exterior angle of an equilateral triangle is 120^o

In a ∆ABC, ∠B > ∠C. Which of AC and AB is longer?

Can we construct a ∆ABC in which AB=5cm, BC=4cm and AC=9cm? Why?

Show that the difference of any two sides of a triangle is less than the third side

In a right ∆ABC, ∠B=90° and D is the mid-point of AC. Prove that BD=AC.