Gujarati
8. Sequences and Series
easy

The sum of infinite terms of the geometric progression $\frac{{\sqrt 2 + 1}}{{\sqrt 2 - 1}},\frac{1}{{2 - \sqrt 2 }},\frac{1}{2}.....$ is

A

$\sqrt 2 {(\sqrt 2 + 1)^2}$

B

${(\sqrt 2 + 1)^2}$

C

$5\sqrt 2 $

D

$3\sqrt 2 + \sqrt 5 $

Solution

(a) $\frac{{\sqrt 2 + 1}}{{\sqrt 2 – 1}},\frac{1}{{\sqrt 2 (\sqrt 2 – 1)}},\frac{1}{2},……$

Common ratio of the series $ = \frac{1}{{\sqrt 2 (\sqrt 2 + 1)}}$

$\therefore $ sum  $ = \frac{a}{{1 – r}} = \frac{{\left( {\frac{{\sqrt 2  + 1}}{{\sqrt 2  – 1}}} \right)}}{{\left( {1 – \frac{1}{{\sqrt 2 (\sqrt 2  + 1)}}} \right)}}$

$ = \frac{{(\sqrt 2 + 1)}}{{(\sqrt 2 – 1)}}.\,\frac{{\sqrt 2 \,(\sqrt 2 + 1)}}{{(1 + \sqrt 2 )}}$$ = \sqrt 2 {(\sqrt 2 + 1)^2}$.

Standard 11
Mathematics

Similar Questions

Start a Free Trial Now

Confusing about what to choose? Our team will schedule a demo shortly.