Angles and lines
Parallel lines and transversals
Triangle and polygon angle sums
Triangles
Pythagorean Theorem and triples
Special right triangles
Similar and congruent triangles
Area formulas, including Heron’s formula
Triangle inequality
Special triangle lines
Medians, angle bisectors, altitudes
Angle Bisector Theorem
Centroid, incenter, circumcenter
Quadrilaterals and polygons
Properties of parallelograms, trapezoids, kites
Regular polygons and interior angles
Circles
Chords, tangents, secants
Inscribed and central angles
Power of a Point
Arc length and sector area
Cyclic quadrilaterals
Trigonometry
Sine, cosine, tangent in right triangles
Law of Sines and Law of Cosines (occasional)
Area as (1/2)ab sin C
Geometric strategies
Area ratios and shaded regions
Dissection and auxiliary lines
Mass points (occasional)