Maths cross word puzzle

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Across
  1. 4. angled triangle triangle that has sides of lenght 3,4,5.what type of traingle is it
  2. 7. year's how many years are there in a decade
  3. 8. what is largest unit of volume
  4. 9. angle angle greater than 180 degree but less than 360 degree
  5. 10. name of the symbol ( ∆)
  6. 12. shape of the brick
  7. 13. all negative numbers are less than what number
  8. 16. theorem most famous theorem of triangle in geometry
  9. 20. mean of the numbers 4,8,6,12
Down
  1. 1. how many furlongs in a mile
  2. 2. Half of the radius
  3. 3. father of mathematics
  4. 5. full form of maths
  5. 6. Half of the circle
  6. 11. who discovered zero
  7. 14. name of the polygon with 8 sides
  8. 15. wallis who discovered infinity symbol ♾️
  9. 17. all natural number's are whole numbers not all whole numbers are natural number's.true or false
  10. 18. smallest perfect number
  11. 19. inches what is one half of single foot