Gujarati
8. Sequences and Series
easy

The first and last terms of a $G.P.$ are $a$ and $l$ respectively; $r$ being its common ratio; then the number of terms in this $G.P.$ is

A

$\frac{{\log l - \log a}}{{\log r}}$

B

$1 - \frac{{\log l - \log a}}{{\log r}}$

C

$\frac{{\log a - \log l}}{{\log r}}$

D

$1 + \frac{{\log l - \log a}}{{\log r}}$

Solution

(d) $l = a{r^{n – 1}}$ $ \Rightarrow $ $\frac{{l}}{{a}}=r^{n-1}$

 $ \Rightarrow $ $1 + \frac{{\log l – \log a}}{{\log r}}=n$

Standard 11
Mathematics

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