Vivian

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Across
  1. 3. a flat shape with seven straight sides and seven angles
  2. 8. a flat shape with eight straight sides and eight angles
  3. 10. a line segment from the center to the midpoint of one of its sides
  4. 12. the intersections of the angular bisectors is the center of it
  5. 14. two circles only contact on one point with overlapped area
  6. 15. polygon with the same interior angles and sides’ lengths.
  7. 17. a flat shape with four straight sides
  8. 18. a flat shape with six straight sides and six angles
  9. 19. the intersecting points of the medians of a triangle
  10. 20. a flat shape with ten straight sides and ten angles
  11. 21. the intersecting point of the angular bisector of a triangle
Down
  1. 1. triangle with the same side length on three sides
  2. 2. the vertexes of the triangles are all on the circle
  3. 4. triangle with the same side length on two sides
  4. 5. a flat shape with twelve straight sides and twelve angles
  5. 6. having four straight equal sides and four angles of 90°
  6. 7. two circles only contact on one point without overlapped area
  7. 9. a flat shape with three straight sides and three angles
  8. 11. a flat shape with five straight sides and five angles
  9. 13. a flat shape with nine straight sides and nine angles
  10. 16. a flat shape with at least three straight sides and angles, and usually five or more