arithmetic or geometric?

State the common difference or ratio and determine a formula for the nth term.

5,10,20,40,...

I got the common difference which is X 2. But I dont get the 2nd part.

harish21

State the common difference or ratio and determine a formula for the nth term.

5,10,20,40,...

I got the common difference which is X 2. But I dont get the 2nd part.

The nth term of a geometric sequence with initial value a and common ratio r is given by $$\displaystyle {a_n} = r \times a^{n-1}$$

So,
The nth term for this sequence would be given by:

$$\displaystyle {a_n} = 5 \times 2^{n-1}$$

masters

MHF Helper
State the common difference or ratio and determine a formula for the nth term.

5,10,20,40,...

I got the common difference which is X 2. But I dont get the 2nd part.
$$\displaystyle a_n=a_1r^{n-1}$$
$$\displaystyle a_n=5(2)^{n-1}$$