WAEC - Further Mathematics (2013 - No. 12)
The fourth term of an exponential sequence is 192 and its ninth term is 6. Find the common ratio of the sequence.
\(\frac{1}{3}\)
\(\frac{1}{2}\)
\(2\)
\(3\)
설명
\(T_{n} = ar^{n - 1}\)
\(T_{4} = ar^{4 - 1} = ar^{3} = 192\)
\(T_{9} = ar^{9 - 1} = ar^{8} = 6\)
Dividing \(T_{9}\) by \(T_{4}\),
\(r^{8 - 3} = \frac{6}{192}\)
\(r^{5} = \frac{1}{32} = (\frac{1}{2})^{5}\)
\(r = \frac{1}{2}\)