Answer
a. 7, 21, 63, 189, 567
b. r = 3
c. see below
Work Step by Step
A geometric sequence is a sequence whose terms are obtained by multiplying each term by the same fixed constant $r$ to get the next term.
A geometric sequence has the form
$a, ar, ar^{2}, ar^{3}, \ldots$
The number $a$ is the first term of the sequence, and the number $r $is the common ratio.
The nth term of the sequence is $\quad a_{n}=ar^{n-1}$
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By comparing the general formula for the n-th term,
$a=7, r=3.$
a. The first five terms
$a_{1}=7$
$a_{2}=7(3)=21$
$a_{3}=21(3)=63$
$a_{4}=63(3)=189$
$a_{5}=189(3)=567$
b. $r=3$
c. graphed in desmos.com (image attached in answer)
