## Geometry: Common Core (15th Edition)

$m \angle 1 = 49^{\circ}$ $m \angle 2 = 131^{\circ}$ $m \angle 3 = 131^{\circ}$
According to theorem 6-19, the base angles of an isosceles trapezoid are congruent; therefore, if one of the base angles is $49^{\circ}$, the other base angle, $\angle 1$, is $49^{\circ}$. If we take a look at the diagram, we see that we essentially have two transversals cutting a pair of parallel lines. The angles formed by each transversal are, in actuality, alternate interior angles; these types of angles are supplementary. Let's set up the equation to find the other two base angles, $\angle 2$ and $\angle 3$: $m \angle 2 = 180 - 49$ Subtract to solve: $m \angle 2 = 131^{\circ}$ If $m \angle 2 = 131^{\circ}$, then $m \angle 3 = 131^{\circ}$ because these two angles are base angles of the isosceles trapezoid and, thus, are congruent.