Math puzzle

1234567891011121314151617181920
Across
  1. 1. Side by side
  2. 3. small device
  3. 9. Change of balance money received
  4. 11. A number that Identifies a position
  5. 13. In the product of a constant
  6. 14. Mathematical constant that is the ratio
  7. 17. The total space taken up
  8. 18. The mathematics of generalized arithmetic
  9. 20. Add,subtract,break apart
Down
  1. 2. The line dividing an angle into two
  2. 4. The distance around a circle
  3. 5. A procedure or set of steps
  4. 6. Gets bigger
  5. 7. The space between two lines
  6. 8. A circumstance, fact or influence
  7. 10. Able to be changed or adapted
  8. 12. A number that divides another number
  9. 15. The length through a straight line
  10. 16. Mathematics involving derivative
  11. 19. The line where two faces meet