Geometry!

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Across
  1. 2. same shape but different size
  2. 6. the longest side of a triangle
  3. 7. measures exactly 90
  4. 8. the point in the middle
  5. 10. a line that splits them into two
  6. 12. add them together and get 180
  7. 13. add them together and get 90
  8. 14. destined to never meet
Down
  1. 1. where it all started...
  2. 3. same shape and size
  3. 4. line AB looks in the mirror
  4. 5. scale it up
  5. 9. equal in measure
  6. 11. going through galaxies! (or in this case, lines)