Answer:
No, the triangular numbers are not a direct variation. There is not a constant of variation between a number and its position in the sequence. The ratios of the numbers to their positions are not equal. Also, the points (1, 1), (2, 3), (3, 6), and so on, do not lie on a line.
Explanation:
this is correct on edge
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Cooperative is the answer that you seen to be looking for
I would say about 10+. It really just depends on if you are planning on writing a long book, or a short book, but in my opinion, it would be 10+.