Answer:
n^2 + 2n.
Explanation:
n = 1 2 3 4 5
term t = 3 8 15 24 35
Diffs = 5 7 9 11
2 2 2 - so the nth term contains n^2.
n^2 = 1 4 9 16 25
t - n^2 = 2 4 6 8 10
This is an arithmetic sequence with nth term = 2 + (n-1)2 = 2n
So the nth term of the quadratic sequence = n^2 + 2n.