Question

recursive formula

Answer 1

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Answer 2

@Shadow

Answer 3

it's important to understand the notation here

t1 = 1 gives you your first term
tn = t_n-1 + n means to get the next term, add the previous term AND the term number (basically, the first term has n = 1, the second term has n = 2, etc.)

so for t2, add the previous term (1) and the term number (2) to get 3. that already narrows us down to choices C and D. try to repeat this process to get t3.