csat-suneung 2024 Q11

csat-suneung · South-Korea · csat__math 4 marks Arithmetic Sequences and Series Telescoping or Non-Standard Summation Involving an AP

For an arithmetic sequence $\{a_n\}$ with nonzero common difference, $$|a_6| = a_8, \quad \sum_{k=1}^{5} \frac{1}{a_k a_{k+1}} = \frac{5}{96}$$ Find the value of $\sum_{k=1}^{15} a_k$. [4 points]
(1) 60
(2) 65
(3) 70
(4) 75
(5) 80

For an arithmetic sequence $\{a_n\}$ with nonzero common difference,
$$|a_6| = a_8, \quad \sum_{k=1}^{5} \frac{1}{a_k a_{k+1}} = \frac{5}{96}$$
Find the value of $\sum_{k=1}^{15} a_k$. [4 points]\\
(1) 60\\
(2) 65\\
(3) 70\\
(4) 75\\
(5) 80

Paper Questions

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