Geometry & Measurement

Angle Relationships

• Parallel lines cut by a transversal: corresponding angles are equal; alternate interior angles are equal; co-interior angles add to 180°.
• Exterior angle of a triangle = sum of the two non-adjacent interior angles.
• Polygon interior angle sum: (n − 2) × 180° where n = number of sides.

Similar & Congruent Figures

Congruent: same shape AND size (all sides and angles equal).
Similar: same shape, proportional sides (angles equal, sides in ratio).

If two triangles are similar with ratio 3:5, then areas are in ratio 9:25 (square the ratio).

Coordinate Geometry

• Slope: m = (y₂ − y₁)/(x₂ − x₁) = rise/run
• Slope-intercept form: y = mx + b (m = slope, b = y-intercept)
• Distance: √[(x₂−x₁)² + (y₂−y₁)²]
• Midpoint: ((x₁+x₂)/2, (y₁+y₂)/2)