Answer
General Term Formula: $a_n=0.0004 \cdot (-10)^{n-1}$
$\\a_{7} = 400$
Work Step by Step
RECALL:
The formula for the general term (nth term) of a geometric sequence is:
$a_n=a_1 \cdot r^{n-1}$
where
r = common ratio
$a_1$ = first term
$a_n$ = nth term
$n$= term number
To find the formula for the general term of the given geometric sequence, perform the following steps:
(1) Solve/find the values of $a_1$ and $r$
The given sequence has:
$a_1 = 0.0004$
$r = \frac{-0.004}{0.0004} =-10$
(2) Substitute the values of $a_1$ and $r$ in the formula above.
Substituting gives:
$a_n = 0.0004 \cdot (-10)^{n-1}$
Therefore, the 7th term of the sequence is:
$a_{7}=0.0004 \cdot (-10)^{7-1}
\\a_{7}=0.0004 \cdot (-10)^6
\\a_{7} = 0.0004 \cdot 1,000,000
\\a_{7} = 400$
