Very tricky thing

123456789101112
Across
  1. 4. 4746x5474
  2. 5. multiplication and use perimeter
  3. 8. has something included with area
  4. 10. add numbers till it becomes a triangle
  5. 11. can be odd or even
  6. 12. 67/898
Down
  1. 1. 9 divided by 4657
  2. 2. add till you get a square number
  3. 3. can be multiplied by 1
  4. 6. 1646+53835
  5. 7. below a whole number
  6. 9. 49794-74879