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Determine the expression for the nth term

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$a_4=11$

Explanation:

Given the sequence $20;17;14;\ldots -103 \dots$ it can be seen that the common difference is $-3$ i.e. $a_{n+1}-a_n=3$

$20-17=3$

$17-14=3$

This is a decreasing sequence i.e. decreasing by 3 with each term.

the fourth term is calculated using the following linear equation:

$14-a_4=3$

$a_4=14-3$

$\therefore a_4=11$

by Platinum (119,106 points)
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The nth term is given by the formula:

$T_n=a+(n-1) d$

where

$a$ is the first term

$d$ is the common difference

$T_n = 20+(4-1)-3$

$T_n =20-9=11$
by Gold Status (31,693 points)

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