Vivian

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Across
  1. 4. having four straight equal sides and four angles of 90°
  2. 9. the intersections of the triangles’ angular bisectors are all on the circle
  3. 11. a flat shape with five straight sides and five angles
  4. 12. a flat shape with three straight sides and three angles
  5. 14. a flat shape with at least three straight sides and angles, and usually five or more
  6. 17. two circles only contact on one point, and they are on the different side
  7. 18. a flat shape with ten straight sides and ten angles
Down
  1. 1. the vertexes of the triangles are all on the circle
  2. 2. polygon with the same interior angles and sides’ lengths.
  3. 3. a flat shape with twelve straight sides and twelve angles
  4. 5. a flat shape with four straight sides
  5. 6. triangle with the same side length on three sides
  6. 7. triangle with the same side length on two sides
  7. 8. a flat shape with eight straight sides and eight angles
  8. 10. a flat shape with six straight sides and six angles
  9. 13. of a regular polygon is a line segment from the center to the midpoint of one of its sides
  10. 15. a flat shape with nine straight sides and nine angles
  11. 16. a flat shape with seven straight sides and seven angles