Here, we want to use an indirect proof to show that the two base angles are congruent
For an isosceles triangle, we have two sides that are equal
So what this mean is that AB and AC are equal
Now, particularly, we can see that the angles face the same side length
Since the angles face the side length and the ratio of how large an angle is corresponds to the length of the side it faces, then we can conclude that the two angles are equal since they face equal side lengths