Math word puzzle

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Across
  1. 4. A pair of matching sides that are placed in the same spot of two different shapes
  2. 7. Divide into two equal parts
  3. 8. Angles that occupy the same relative position with each other
  4. 9. Cause, explanation, or justification for an event.
  5. 10. a theorem connected by a short proof to an existing theorem.
  6. 13. the angles that do not share a vertex with a given exterior angle
  7. 15. A definite or clear expression of speech or writing
  8. 17. The angles that lie inside a polygon
  9. 18. an extra line needed to complete a proof in plane geometry.
  10. 19. Triangles having corresponding sides and angles to be equal.
Down
  1. 1. An angle of a polygon is formed by two adjacent sides
  2. 2. True statements that combine the hypothesis and the conclusion with the key words 'if and only if.
  3. 3. the angle between a side of a rectilinear figure and an adjacent side extended outward
  4. 4. A statement joining two events together based on a condition in the form of “If something, then something
  5. 5. Uses side side side theorem
  6. 6. an isosceles triangle is a triangle that has two sides of equal length
  7. 11. Is when a shape is moved without changing the shape or size
  8. 12. Two things that are the same
  9. 14. The side of a polygon or a geometric figure that is enclosed by two consecutive vertices
  10. 16. The converse of an if-then statement is such that the IF and THEN parts are swapped