Maths crossword

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Across
  1. 5. a number when multiplies with itself three times becomes this
  2. 6. a number with a power 1 or more
  3. 7. additive identity of rational numbers
Down
  1. 1. polygon that has minimum number of straight line segments
  2. 2. a trick to find cube root
  3. 3. a polygon with 10 elements
  4. 4. a number multiplied with itself 2 times becomes this