Question

Find an equation for the nth term of a geometric sequence where the second and fifth terms are -8 and 512, respectively.
answer choices

an = 2 • (-4)^n + 1
an = 2 • 4^n - 1
an = 2 • (-4)^n - 1
an = 2 • 4^n

Answer 1

You can just do a simple plug and chug process here

Check out the 2nd answer choice, lets work with it...you know the second term is -8 so

\[\large a_n = 2\times 4^{n-1}\]
becomes
\[\large a_2 = 2\times 4^{2-1}\]
\[\large a_2 = 2\times 4^1\]
\[\large a_2 = 2\times 4 = 8\]

This is not the correct answer choice since we know the second term SHOULD be -8 not 8

So that eliminates both B and D as answer choices

Answer 2

would it be c