1 , 3 , 6 , 10 , 15 1) What is the nth term of the sequence?

2) Use the nth term to work out the 21st term of the sequence.

First difference,

Second difference,

Third difference,

And so on.

Assuming the pattern holds on, we see that

i-th difference,

Then, nth term is,

Now, the 21st term in the sequence is,

step-by-step explanation:

through just a quick inspection, one can see that the graph of this cubing function starts in quadrant iii and ends in quadrant i.   when x = 0, y = 3, so the y-intercept is (0, 3).

if graphs are part of the problem statement, share them.   .