Name the Mathematicians

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Across
  1. 2. Discovered subdivision of Geometry
  2. 4. a^2+b^2=c^2
  3. 5. A=[s(s-a)(s-b)(s-c)]^0.5
  4. 7. Father of Geometry
Down
  1. 1. E=mc^2
  2. 2. Father of Algebra
  3. 3. logxy=logx+logy
  4. 6. i^2=-1