Question

problem 12: (first taught in lesson 29)
from this given statement, select the definition, property, postulate, or theorem that justifies the prove statement.
given: △abc, mab = 9, and mbc = 9
prove: △abc is isosceles.

Explanation:

An isosceles triangle is defined as a triangle with at least two sides of equal length. Here, in $\triangle ABC$, since $m\overline{AB}=9$ and $m\overline{BC} = 9$, two - sides are of equal length, so by the definition of an isosceles triangle, $\triangle ABC$ is isosceles.

Answer:

Definition of an isosceles triangle