Question

Help??
Find an explicit rule for the nth term of a geometric sequence where the second and fifth terms are -12 and 768, respectively.

Answer 1

2nd term = a1 r
5th term = a1 r^4 where r is the common ratio and a1 = first term

so 5th/2nd term = a1 r^4 / a1 r = r^3 = 768/-12 = = -64

so r^3 = -64

Answer 2

now you can find the common ratio r
r = cube root of -64

Answer 3

can you work that out? use ur calculator

Answer 4

yes thank you!

Answer 5

yw

first term will be -12/-4

nth term = a1 r^(n-1)

Answer 6

So the answer would be 3*(-4)^n-1 @welshfella