Question

Can anyone help with sequences? Medal to who can help.

Find an explicit rule for the nth term of the sequence. 2, -8, 32, -128, ...

answer choices:
an = 2 ⋅ 4^n+1

an = 2 ⋅ (-4)^n

an = 2 ⋅ 4^n-1

an = 2 ⋅ (-4)^n-1

n-1 means number before what ever n is right?
n means the number? I am confused. Thanks to anyone who can help

Answer 1

think of n as "now"; and n-1 as "then" so yes

Answer 2

well N means the Nth term.
Yes n-1 means the number before the number n.
The answer here would be D.

Example -

A1 = 2.

Now for A2 if we use An = 2.(-4)^n-1, we have

A2 = 2.(-4)^2-1

which is 2.(-4)^1 = 2.-4 = -8.

Similarly A3 = 2.(-4)^3-1

=> 2.(-4)^2 = 2.16 = 32.

Answer 3

OH! so, N is the position of the number in the sequence?

Answer 4

Because if 2 was position 1
1-1 would be 0 2-0 would be 2
which is the first term
and so on!

Answer 5

if the sequence starts with n=1, then yes

Answer 6

Thanks so much guys!