The fourth term of a geometric sequence is 2 and the sixth term is 8.
FURTHER MATHEMATICS
WAEC 2011
The fourth term of a geometric sequence is 2 and the sixth term is 8. Find the common ratio.
- A. \(\pm 1\)
- B. \(\pm 2\)
- C. \(\pm 3\)
- D. \(\pm 4\)
Correct Answer: B. \(\pm 2\)
Explanation
\(T_{n} = ar^{n - 1}\) (Exponential sequence)
\(T_{4} = ar^{3} = 2 .... (1)\)
\(T_{6} = ar^{5} = 8 ......(2)\)
Divide (2) by (1),
\(\frac{ar^{5}}{ar^{3}} = \frac{8}{2} \)
\(r^{2} = 4\)
\(r = \pm 2\)
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