Elements of stereometry

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Across
  1. 2. The formula V=a*b*c is used to calculate V of?
  2. 5. A triangular pyramid is called?
  3. 6. A prism based on regular polygons
  4. 7. the formula 2piR(R+H) serves to calculate P of
  5. 9. Height lowered from the top of the pyramid
  6. 10. The straight cylinder is called
  7. 12. What is the name of the segment whose endpoints are two vertices of the prism that do not lie on the same wall
Down
  1. 1. ribbed body or
  2. 3. M-side surface or
  3. 4. P=Rπ(R+S) is area for
  4. 8. What kind walls are the triangles of the pyramid?
  5. 11. What are the circles of the cylinder called?