This is an example of a geometric sequence. To find for the nth term, we use the formula:
an = a1 r^(n – 1) ---> 1
Where:
a1= 1st term of the sequence = -a
r = common ratio
To find for the common ratio r, we divide the 2nd term with the 1st term (we can also divide the 3rd term with the 2nd term; we can use any 2 terms as long as they are in succession.)
r = a^2 / -a
r = -a
Substituting a1 and r in equation 1:
an = -a (-a)^(n-1)
Therefore the answer: B) -a(-a)n-1
