I am reading about uniform circular motion currently, but I am sort of confused by this paragraph: "We next determine the magnitude of the centripetal centripetal (radial) acceleration, ar. Because CA in fig. 5-2a is perpendicular to V1, and CB is perpendicular to V2, it follows that the angle Δθ, defined as the angle between CA and CB, is also the angle between V1 and V2. Hence the vectors V1, V2, and ΔV in fig. 5-2b form a triangle that is geometrically similar to the triangle CAB in fig. 5-2a" I have attached the two figures. Why are the two triangles similar?