arithmetic or geometric?

May 2005
82
0
I LIVE IN QUEBEC,CANADA
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.
 
Feb 2010
1,036
386
Dirty South
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:

\(\displaystyle {a_n} = 5 \times 2^{n-1}\)
 
  • Like
Reactions: blame_canada100

masters

MHF Helper
Jan 2008
2,550
1,187
Big Stone Gap, Virginia
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.
Hi blame_canada100,

You didn't find a common difference; you found a common ratio.

\(\displaystyle a_n=a_1r^{n-1}\)

\(\displaystyle a_n=5(2)^{n-1}\)

Continue....
 
  • Like
Reactions: blame_canada100