Gerta's crossword puzzle

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Across
  1. 4. ≅
  2. 6. when 2 lines intersect that are opposite to each other
  3. 9. 2 angles that have a sum of 90°
  4. 11. ∟
  5. 14. ⊥
  6. 15. 2 angles that have a sum of 180°
Down
  1. 1. If AB ≅ CD then CD ≅ AB
  2. 2. to flip an object to across a line
  3. 3. ∠
  4. 5. 90° rotation counterclockwise,180° rotation 270°
  5. 7. two types: rotational and line
  6. 8. lines line that lie on the same lie and never cross
  7. 10. three sides with equal length
  8. 12. Two angles and the side between them are congruent
  9. 13. center of the triangles intersection points