Find the terms $a_{2}, a_{3}, a_{4}$ and $a_{5}$ of a geometric sequence if $a_{1} = 10$ and the common ratio $r = - 1$

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Solution

We know the terms in geometric series are in the form $a r, a r^{2}, a r^{3}, a r^{4}, a r^{5}, . . . .$
Given, $a_{1} = 10, r = - 1$
$a_{2} = a_{1} r = 10 (- 1) = - 10$
$a_{3} = a_{1} r^{2} = 10 {(- 1)}^{2} = 10$
$a_{4} = a_{1} r^{3} = 10 {(- 1)}^{3} = - 10$
$a_{5} = a_{1} r^{4} = 10 {(- 1)}^{4} = 10$

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