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The sum of first $n$ terms of an A.P. is given by $S_n = 4n^2 - n$. Find the $25^{th}$ term of this A.P.
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Solution:
$S_n = 4n^2 - n$
$a_{25}= S_{25} - S_{24}$ (1/2 Mark)
$= [4(25)^2-25] - [4(24)^2 – 24]$ (1 Mark)
$= 195$ (1/2 Mark)
$S_n = 4n^2 - n$
$a_{25}= S_{25} - S_{24}$ (1/2 Mark)
$= [4(25)^2-25] - [4(24)^2 – 24]$ (1 Mark)
$= 195$ (1/2 Mark)