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The seventh and tenth terms of a geometric sequence are $7$ and $21$, respectively. What is the $13$th term of this progression?

 Mar 4, 2021
 #1
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a + 7d = 7

a + 10d = 21

==> d = 2, a = -7

 

13th term = a + 13d = 19.

 Mar 4, 2021

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