Geometry!

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Across
  1. 2. a four sided figure with two pairs of parallel sides
  2. 4. a four sided figure where all angles are 90 degrees
  3. 6. an angle that is 90 degrees
  4. 10. an angle that is 180 degrees
  5. 11. the distance from one side of a circle to the other, which goes through the center
  6. 13. a triangle with three different side lengths
  7. 14. a triangle with three equal side lengths
  8. 16. a one dimensional shape
  9. 17. something that has zero dimensions
  10. 20. a four sided platonic shapes
  11. 21. a four sided figure where all sides are equal and all angles are 90 degrees
Down
  1. 1. a line that just barely touches a circle’s edge, and is perpendicular to the radius
  2. 2. a two dimensional shape
  3. 3. an angle that is less than 90 degrees
  4. 5. an eight sided platonic shape
  5. 6. a four sided figure with 4 equal side lengths
  6. 7. The ratio of the distance around a circle to the radius
  7. 8. a four sided shape
  8. 9. the distance around a circle
  9. 12. a four sided figure with two sets of adjacent congruent sides
  10. 15. a triangle with two equal side lengths
  11. 18. an angle that is greater than 90 degrees but less than 180 degrees
  12. 19. a four sided figure with one pair of parallel sides