Question

Find the sum of n terms of GP:$\sqrt{7},\sqrt{21},3\sqrt{7},...n$ terms.

Answer 1

$S=\sqrt{7}+\sqrt{21}+3\sqrt{7}.....$

here $a=\sqrt{7}$

$r=\sqrt{3}$

$\therefore$ sum of G.P = $\frac{a(r^n-1)}{r-1}$

$\therefore S=\frac{\sqrt{7}\left(\right(\sqrt{3}{)}^n-1)}{(\sqrt{3}-1)}$

$\therefore S=\sqrt{7}\frac{\left(\right(\sqrt{3}{)}^n-1)}{(\sqrt{3}-1)}$