Use angle relationships for intersecting lines, perpendicular lines, and parallel lines cut by a transversal to determine unknown measures with vertical, corresponding, alternate, linear-pair, and supplementary relationships. Apply triangle angle sums, exterior-angle and isosceles relationships, and polygon angle-sum formulas to determine unknown angles, including angles in regular and irregular convex polygons. Classify triangles by angle and side lengths, apply the Pythagorean theorem to find unknown side lengths, and use its converse to determine whether a triangle is right.