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

We call the top of the triangle the point x, y, and we put one corner of the triangle at the origin. Since it is isosceles, we find the slopes: $m_1 = \frac{0-0}{a-0}=0$ $m_1 = \frac{b-0}{a-a}$=undefined Since one slope is undefined and one slope is vertical, one line is vertical, and the other is horizontal. Thus, the two lines are perpendicular.