If 2,(k+1),8,... form an exponential sequence (GP), find the values of k.
FURTHER MATHEMATICS
WAEC 2014
If 2,(k+1),8,... form an exponential sequence (GP), find the values of k.
- A. -3 and 5
- B. 5 and -5
- C. 3 and -3
- D. -5 and 3
Correct Answer: D. -5 and 3
Explanation
Given an exponential sequence, say \(a, b, c,...\), as consecutive terms, then \(\sqrt{a \times c} = b\).
\(\therefore 2, (k+1), 8 \implies \sqrt{2 \times 8} = k + 1\)
\(k + 1 = \pm{4} \implies k = \text{-5 or 3}\)
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