## Elementary Geometry for College Students (6th Edition)

Each base angle has a measure of $55^{\circ}$
By definition of isosceles triangles, the two base angles are equal. Also, the sum of the three angles of a triangle is $180^{\circ}$ Let $x$ be the measure of each base angle. $x + x + 70^{\circ} = 180^{\circ}$ $2x = 180^{\circ}- 70^{\circ}$ $2x = 110^{\circ}$ $x = \frac{110^{\circ}}{2}$ $x = 55^{\circ}$ Each base angle has a measure of $55^{\circ}$