WORDSPLAY-MATHS FIESTA 2K22

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Across
  1. 4. 1/2×diagonal×(sum of the height of two triangles)
  2. 6. .
  3. 7. .
Down
  1. 1. e^ix = cosx + isinx (Who proposed??)
  2. 2. {1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, ...} Which kind of sequence is this?
  3. 3. Who proved that the value of π lies between 3 + 1/7 (approx. 3.1429) and 3 + 10/71 (approx. 3.1408)
  4. 5. How do we write 2022 in roman