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