In the triangle in question, there are 2 sides marked as congruent. That means, by the Isosceles Triangle Theorem, that the angles across from those congruent sides are also congruent. Now that we have that out of the way, we need to figure out what those angles are. 110 is an exterior angle. That means that its supplement, the angle it forms that 180 degree angle with, is 180-110 or 70 degrees. That angle is the same measure as angle 1, so angle 1 is 70 degrees.
