Find an infinite G.P. whose first term is 1 and each term is the sum of all the terms which follow it.
Question:
Find an infinite G.P. whose first term is 1 and each term is the sum of all the terms which follow it.
Solution:
Here, first term, a = 1
Common ratio = r
$\therefore a_{n}=\left[a_{n+1}+a_{n+2}+a_{n+3}+\ldots \ldots \infty\right] \forall n \in N$
$\Rightarrow a r^{n-1}=a r^{n}+a r^{n-1}+\ldots \ldots \infty$
$\Rightarrow r^{n-1}=\frac{r^{n}}{1-r} \quad$ [Putting $a=1$ ]
$\Rightarrow r^{n-1}(1-r)=r^{n}$
$\Rightarrow 1-r=r$
$\Rightarrow 2 r=1$
$\Rightarrow r=\frac{1}{2}$
Thus, the infinte G.P is $1, \frac{1}{2}, \frac{1}{4}, \ldots \infty$.