How do you find nth term rule for $a_2=28$ and $a_5=-1792$ ?

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Answer 1 · 2016-08-17T22:33:51

$a_n = -7(-4)^(n-1)$

The difference between the number implies this is a GP.

$a_5 = ar^4 = -1792$
$a_2 = ar= 28$

Divide the terms: $a_5/a_2 = (ar^4)/(ar) = (-1792)/28$

$(cancelar^4)/(cancelar) = -64$

$r^3 = -64$

$r = -4$

$a_1 = 28/(-4) = -7$

$:. a_n = -7(-4)^(n=1)$

How do you find nth term rule for a_2=28a_2=28 and a_5=-1792a_5=-1792?