8. Sequences and Series
medium

गुणोत्तर श्रेणी $\frac{5}{2}, \frac{5}{4}, \frac{5}{8}, \ldots$ का $20$ वाँ तथा $n$ वाँ पद ज्ञात कीजिए।

A

$\frac{5}{{{{(2)}^{20}}}},\frac{5}{{{{(2)}^n}}}$

B

$\frac{5}{{{{(2)}^{20}}}},\frac{5}{{{{(2)}^n}}}$

C

$\frac{5}{{{{(2)}^{20}}}},\frac{5}{{{{(2)}^n}}}$

D

$\frac{5}{{{{(2)}^{20}}}},\frac{5}{{{{(2)}^n}}}$

Solution

The given $G.P.$ is $\frac{5}{2}, \frac{5}{4}, \frac{5}{8}, \ldots .$

Here, $a=$ First term $=\frac{5}{2}$

$r=$ Common ratio $=\frac{5 / 4}{5 / 2}=\frac{1}{2}$

$a_{20}=a r^{20-1}=\frac{5}{2}\left(\frac{1}{2}\right)^{19}=\frac{5}{(2)(2)^{19}}=\frac{5}{(2)^{20}}$

$a_{n}=a r^{n-1}=\frac{5}{2}\left(\frac{1}{2}\right)^{n-1}=\frac{5}{(2)(2)^{n-1}}=\frac{5}{(2)^{n}}$

 

Standard 11
Mathematics

Similar Questions

Start a Free Trial Now

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