math
posted by matt on .
the third and fourth terms of the sequence are 21 and 38. If the second differences are a constant 2, what are the first five terms of the sequence?

The 1st difference between terms 3 and 4 is 17
The differences and the sequence are thus
2 2 2 2 2 2 2 ...
13 15 17 19 21 23 ...
7 6 21 38 57 78 101 ...