Question

Find a12 given the geometric sequence 2, -6, 18, -54, ...

Answer 1

Given the following geometric sequence:

`2,-6,18,-54,........`

We will find a12

We will use the following formula:

`a_n=a*r^(n-1)`

where a = the first term = 2

r = the common ratio = -6/2 = -3

To find a12, we will substitute n = 12

So,

`a_(12)=2*(-3)^(12-1)=2*(-3)^(11)=-354,294`

So, the answer will be A. -354,294