Jambmaths question:
Evaluate $\tfrac{1}{2}-\tfrac{1}{4}+\tfrac{1}{8}-\tfrac{1}{16}+---$
Option A:
$\tfrac{2}{3}$
Option B:
0
Option C:
$-\tfrac{2}{3}$
Option D:
$-1$
Jamb Maths Solution:
$\begin{align} & a=\tfrac{1}{2} \\ & r=\frac{-\tfrac{1}{4}}{\tfrac{1}{2}}=-\tfrac{1}{2} \\ & {{S}_{\infty }}=\frac{a}{1-r}=\frac{\tfrac{1}{2}}{1-(-\tfrac{1}{2})}=\frac{\tfrac{1}{2}}{1+\tfrac{1}{2}}=\frac{\tfrac{1}{2}}{\tfrac{3}{2}}=\frac{1}{3} \\\end{align}$
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