Geometry I

Strengthen your foundations in geometry with angles, triangles, and polygons.

Triangles and Hexagons

Strategic Geometry

Driving on a Polygon

Angle Hunting Axioms

Advanced Mental Shortcuts

Internal Angles in a Polygon

Invariant Angle Sets

Advanced Angle Hunts

The Triangle Inequality

Congruent and Similar Triangles

Bass Fishing

Curry's Paradox

Composite Figure Warm-ups

Adding Lines and Grids

Complementary Areas

Inclusion and Exclusion

Invariant Areas

Angles of Regular Polygons

Is It Regular?

Polygon Areas and Lengths

Matchstick Polygons



Geometric Stumpers

Challenging Composites

Coordinate Geometry

Advanced Angle Hunting

Applying the Pythagorean Theorem

Course description

In this course, you'll solve delightful geometry puzzles and build a solid foundation of skills for problem-solving with angles, triangles, and polygons. You'll also improve your visual intuition and learn how to come up with clever, creative solutions to tough challenges. This course is the perfect place to start (or continue) your exploration of geometry if you know how to measure angles and calculate the areas of rectangles, circles, and triangles; and want to learn the next level of geometric problem-solving techniques. Additionally, this is a great course to take if you want to strengthen your geometric intuition in preparation for taking a geometry or design course in school. You'll also need to use a little bit of fundamentals-level algebra in this course, but nothing more advanced than two-variable equations, squares, and square roots.

Topics covered

  • Angle Axioms
  • Angle Hunting Shortcuts
  • Composite Area
  • Complementary Areas
  • Curry's Paradox
  • Invariant Areas
  • Polygon Angles
  • Regular Polygons
  • Stellations
  • The Triangle Inequality
  • Triangle Congruence
  • Triangle Similarity


  • Measuring with Geometry