WAEC - Further Mathematics (2006 - No. 13)
Find the sum of the exponential series \(96 + 24 + 6 +...\)
144
128
72
64
คำอธิบาย
\(S_{\infty} = \frac{a}{1 - r}\) (for an exponential series)
\(r = \frac{24}{96} = \frac{6}{24} = \frac{1}{4}\)
\(S_{\infty} = \frac{96}{1 - \frac{1}{4}} = \frac{96}{\frac{3}{4}}\)
= \(\frac{96 \times 4}{3} = 128\)