9514 1404 393
Answer:
63
Step-by-step explanation:
The number of seats in a row will give an arithmetic sequence:
6, 9, 12, 15, ...
The first term is 6; the common difference is 3. The general term is ...
an = a1 +d(n -1) . . . . . . n-th term of sequence with first term a1, difference d
The 20th term of the sequence is ...
a20 = 6 +3(20 -1) = 6 +57 = 63
There would be 63 seats on the 20th row.
Answer:
triangular pyramid
Step-by-step explanation:
Let's make the central triangle the "base", or the bottom face, of our polyhedron. Try to visualise what will happen if we fold up the three triangles so that their top vertices meet at the center top (see diagram).
If we can do that, we'll see that it's a pyramid with a triangular base, so it's a triangular pyramid.