Geometry puzzle

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Across
  1. 1. A line that goes through the circle
  2. 5. A solid object with two identical ends and flat sides
  3. 10. The distance from the center of the circle to the edge
  4. 12. a branch of mathematics concerned with relationships between angles and ratios of lengths
  5. 15. v=π × r² × (h/3)
  6. 16. The largest arc in a circle
  7. 18. triangle with at least two equal sides
  8. 19. base x height
Down
  1. 1. when one shape is identical to the other shape when it is moved, rotated, or flipped.
  2. 2. a2+b2=c2
  3. 3. two lines in the same plane that are at an equal distance from each other and never meet.
  4. 4. Quadrilateral, Decagon, Dodecagon, Concave polygon
  5. 6. two figures having the same shape
  6. 7. half of a sphere
  7. 8. activity to do during a windy day
  8. 9. A line segment connecting two points on a curve
  9. 11. rise over run
  10. 13. 1:2
  11. 14. The size of a surface
  12. 17. extends endlessly in both directions