Math crossword puzzle

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Across
  1. 2. What is a straight line with a 180-degree angle also known as?
  2. 5. The theorem can be written as an equation relating the lengths of the sides a, b and the hypotenuse c. But it only applies to the right triangle. After which Greek philosopher the theorem was named?
  3. 6. What is the term for natural numbers that cannot be evenly divided by any other natural number except one and itself?
  4. 8. What polygon has five sides?
  5. 9. What is the opposite of addition?
Down
  1. 1. What electronic device is used to perform calculations, ranging from basic arithmetic to complex mathematics?
  2. 3. What is it called when in geometry a triangle has two sides of equal length?
  3. 4. What is it called when something is boundless, endless, or larger than any natural number? It is often denoted by the symbol ∞?
  4. 5. It is an irrational number, approximately equal to 3.14159. The number appears in many formulas across mathematics and physics. What number is it?
  5. 7. What is the term for a number that is the result of dividing one quantity by another?