Question 13 and 14, Exercise 4.1
Solutions of Question 13 and 14 of Exercise 4.1 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 13
Find the indicated term of the sequence. $a_{n}=(3 n+4)(2 n-5) ; a_{7}$
Solution.
Do yourself.
Question 14
Find the indicated term of the sequence. $a_{n}=(-1)^{n-1}(3.4 n-17.3) ; a_{12}$
Solution.
Given:
$$a_n = (-1)^{n-1}(3.4n - 17.3).$$
Then
\begin{align*}
a_{12} &= (-1)^{12-1}(3.4 \cdot 12 - 17.3) \\
&= (-1)^{11}(40.8 - 17.3) \\
&= (-1)^{11}(23.5) \\
&= -23.5
\end{align*}
Hence $a_{12} =-23.5 $ 
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