The general formula for determining the nth term of a geometric sequence is expressed as
an = ar^(n - 1)
where
a1 represents the first term
n represents the number of terms
r represents the common ratio
From the information given,
a1 = 5, r = - 1
Since we are looking for the 12th term, a12, n = 12
Thus, we have
a12 = 5(-2)^(12 - 1)
a12 = 5(-2)^11
a12 = - 10240