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Answer 1 · 2018-05-10T19:23:05

Tn = $3 \cdot 2^{n - 1}$ $3*2^(n-1)$

3, 6, 12, 24....

a = 3 First term
r = $\frac{6}{3}$ $6/3$ = 2
n = ?

Tn = $a . r^{n - 1}$ $a.r^(n-1)$ = $3 \cdot 2^{n - 1}$ $3*2^(n-1)$

Answer 2 · 2018-05-10T19:29:59

The fourth selection $t_{n} = 3 {(2)}^{n - 1}$ $t_n = 3(2)^(n-1)$

Given:

$3,6,12,24,...$

Starting with $n = 1$

The first selection:
$t_1 = -2(3)^(1-1) = -2 larr$ does not match so we reject it

The second selection:

$t_1 = 2(3)^(n-1) = 2 larr$ does not match so we reject it

The third selection:

$t_1 = -3(2)^(1-1) larr$ does not match so we reject it

The fourth selection:

$t_1 = 3(2)^(1-1) = 3$
$t_2 = 3(2)^(2-1) = 6$
$t_3 = 3(2)^(3-1) = 12$
$t_4 = 3(2)^(4-1) = 24$

All 4 terms match.