How do you find the 5th term of a geometric sequence whose first term is 4 and whose common ratio is -2?

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Answer 1 · 2018-07-17T08:49:53

Two ways to arrive to result:

One way is calculate the 5th term applying definition of geometric sequence:

$a_1=4$
$a_2=4·(-2)=-8$
$a_3=(-8)·(-2)=16$
$a_4=16·(-2)=-32$
$a_5=(-32)·(-2)=64$

and so on

Other way is apply general term of a geometric sequence

$a_n=a_1·r^(n-1)$

For n=5, we have $a_5=4·(-2)^4=64$