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 \(\pm 4\)
waec 2011furthermathematics

The correct answer is B. \(\pm 2\)

\(T_{n} = ar^{n - 1}\) (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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