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What is the 20th term of the arithmetic sequence 5, -1, -7, ?

1 Answer

Jul 27, 2015

$= a_{20} = - 109$ $=a_20=color(blue)(-109$

Explanation:

The arithmetic sequence is
$5, - 1, - 7$ $5, -1, -7$

The common difference $d$ $d$ of this sequence is
$d = - 1 - 5 = - 6$ $d=-1-5 = -6$

The formula for $n_{t h}$ $n_(th)$ of an arithmetic series is:
$a_{n} = a + (n - 1) (d)$ $color(blue)(a_n = a+(n-1)(d)$

Here, $a = 5, d = - 6, n = 20$ $a = 5, d=-6, n=20$

So, $a_{20} = 5 + 19 (- 6$ $a_20 = 5 +19(-6$ )

$= 5 - 114$ $=5-114$
$= - 109$ $=color(blue)(-109$

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