If $S_n=an^2+bn+c$, then the $n$th term $t_n$ of the sequence is
A$t_n=S_n+S_{n-1}$
B$t_n=S_n-S_{n-1}$
C$t_n=\dfrac{S_n}{n}$
D$t_n=S_{n+1}-S_n$
Answer & Solution
Correct answer: B. $t_n=S_n-S_{n-1}$
By definition, the $n$th term equals the sum of the first $n$ terms minus the sum of the first $(n-1)$ terms. Therefore $t_n=S_n-S_{n-1}$. Option D gives the $(n+1)$th term, not the $n$th term.
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