Question

Given: Triangle ABC is an isosceles triangle where AB = BC

Answer 1

We have to find the reason for statement 3, which is:

`m\angle ABD=m\angle CBD`

This angles are the angles that are formed after the bisection of ∠ABC.

As BD is an angle bisector, then the angle is divided into two equally measured angles, that are ∠ABD and ∠CBD.

Then, the reason for this statement is the definition of angle bisector.

Answer: definition of angle bisector [Option A]