Question:
Which term of the GP $\sqrt{3}, 3,3 \sqrt{3} \ldots$ is $729 ?$
Solution:
Given GP is $\sqrt{3}, 3,3 \sqrt{3} \ldots$
The given GP is of the form, $a, a r, a r^{2}, a r^{3} \ldots .$
Where $r$ is the common ratio.
First term in the given GP, $a_{1}=a=\sqrt{3}$
Second term in GP, $a_{2}=3$
Now, the common ratio, $r=\frac{a_{2}}{a_{1}}$
$r=\frac{3}{\sqrt{3}}=\sqrt{3}$
Let us consider 729 as the $n^{\text {th }}$ term of the GP.
Now, $\mathrm{n}^{\text {th }}$ term of GP is, $\mathrm{a}_{\mathrm{n}}=\mathrm{ar}^{\mathrm{n}-1}$
$729=\sqrt{3}(\sqrt{3})^{n-1}$
$\sqrt{3}^{n}=\sqrt{3^{12}}$
$n=12$
So, 729 is the $12^{\text {th }}$ term in GP.