The $n$ th term of a sequence is given by $u_n = an^2 + bn + c$. The first three terms of this s

Question

The $n$ th term of a sequence is given by $u_n = an^2 + bn + c$. The first three terms of this sequence of numbers are $2$, $6$ and $12$. Find the values of $a$, $b$ and $c$.[3] Given that $\sum_{n=1}^{N} \frac{1}{u_n} = 1 - \frac{1}{N+1}$, find $\sum_{n=8}^{\infty} \frac{1}{u_n}$.[3]

Accepted Answer

(a) $a=1,\ b=1,\ c=0$. (b) $\frac{1}{8}$.

2025 CJC P1 Q2

2025 CJC P1 Q2

Solution:

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