Which relationship is always true for the angles r, x, y, and z of triangle ABC? A triangle is shown with a leg extending past the top vertex. The vertices are labeled ABC. Angle y is located inside the triangle at vertex B. Angle z is located inside the triangle at vertex C. Angle x is located outside the triangle between beside vertex A and the extended leg. Angle r is located inside the triangle at vertex A. x + z = y 180 degrees − x = r x + y + z = 180 degrees x + y + z = 90 degrees