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Geometry Puzzles!

posted Feb 10, 2015, 9:33 AM by Michael Dreyfus-Pai   [ updated Sep 11, 2016, 3:03 PM by Karen McMillan ]
Here are some geometry activities you can try out next:

Khan Academy

At you will find some recommended skills to practice.


Proofs are like puzzles. To prove something in geometry, you can only use other geometry facts you already know. You can't use measuring in a proof!

1) Angles in a trapezoid

  • Draw a pair of parallel lines
  • Draw TWO transversals. Do not connect them.
  • Pairs of supplementary angles
  • What's the sum of the interior angles? How can you know this WITHOUT MEASURING THEM?

2) Angles in a triangle

  • Using lines (not line segments), draw a triangle
  • Select a vertex and the line opposite that vertex. Construct a parallel line.
  • Using what you know about parallel lines cut by a transversal, find the two ? angles.
  • What is the sum of the interior angles of the triangle? How can you know this without measuring them?