I'm sigma

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Across
  1. 3. a shape with many sides
  2. 4. L times W
  3. 8. all the sides of a 2-D object
  4. 9. lines, lines that cross each other
Down
  1. 1. (x,y)
  2. 2. shape with triangle sides and a square bottom
  3. 5. all the sides of a 3-D object
  4. 6. polygon,
  5. 7. 3-D object with a triangle bottom