help with series (geometric & arithmetic) (1 Viewer)

[thanhrox]

i have so much trouble telling the difference between a geometric and arithmetic series.

how do i tell the difference between them?

cheers

 

[tommykins]

Arithmetic have a common difference.
Geometric have a common ratio.

Arithmetic - 1,3,5,7,9,11,13....
If you minus 13-11, you get 2.
If you minus 11-9, you get 2.
Thus the common difference is 2. An algebraic way to put it is
Tn+1 - Tn = d where d is the common difference, Tn+1 is the n+1 term and Tn is the nth term.

Geometric is where there is a common ratio.
Consider - 2,4,8,16,32,64,128....
If you divide the Tn+1 term by the Tn term, you get r which is the common ratio.
In this case, 128/64 = 2.
64/32 = 2
4/2 = 2.

So on and so forth.

 

[Timothy.Siu]

yeah wat he sed
and also, if they ask to find limiting sum or if its a money problem its geometric as well