====== Question 14 and 15, Exercise 4.4 ======
Solutions of Question 14 and 15 of Exercise 4.4 of Unit 04: Sequence and Series. This is unit of Model Textbook of Mathematics for Class XI published by National Book Foundation (NBF) as Federal Textbook Board, Islamabad, Pakistan. 

=====Question 14=====
Find the nth term of the geometric sequence if $a_{1}=4, n=3, r=5$.

** Solution. **

Given $a_{1}=4, n=3, r=5$.\\
General term of the geometric series is given by
$$a_{n}=a_{1} r^{n-1}.$$
Thus
\begin{align*}
a_3&= 4\times 5^2 \\
&=4\times 25 = 100. 
\end{align*}
Hence $a_3=100$.




=====Question 15=====
Find the nth term of the geometric sequence if $a_{1}=2, n=5, r=2$.

** Solution. **

Given $a_{1}=2$, $n=5$, $r=2$.\\
General term of the geometric series is given by
$a_{n}=a_{1} r^{n-1}.$
Thus
\begin{align*}
a_5 &= 2 \times 2^{5-1} \\ 
&= 2 \times 2^4 \\ 
&= 2 \times 16 = 32.
\end{align*}
Hence $a_5=32$.








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