Geometry: Lines, Angles & Triangles Angle Relationships Vertical angles are equal Supplementary angles add to 180° Complementary angles add to 90° Parallel lines + transversal: alternate interior angles are equal, corresponding angles are equal Triangle Properties Angle sum = 180° Exterior angle = sum of two remote interior angles Triangle inequality: any side < sum of other two sides Special Triangles 30-60-90 → sides x : x√3 : 2x | 45-45-90 → sides x : x : x√2 Area & Perimeter Area = ½ × base × height SAT Tips Draw and label diagrams Look for special triangles hidden in complex figures Use the given reference formulas at the start of each SAT math section