First you need to find out if the set is an arithmetic sequence or a geometric sequence.
Is it Arithmetic?To find out if the set is arithmetic, the set has to have a common deference. You check for a common difference by taking the consecutive number and subtracting the number that comes before it. So
12 - 72 = -60
2 - 12 = -10
The numbers are not the same so there is no common difference. So the set is not arithmetic.
Is it Geometric?To find out, you need to see if there is a common ratio between the numbers.
Take the consecutive number 12 and divide it by 72 and so on.
12/72 = .1666666667 =

2/12 = .1666666667 =

They are the same so the set is geometric.
Now that you know the set is geometric, it is time to write a recursive formula for 72,12,2
To write this formula, you need to state the first term and use the common ratio that was found, which is
State the first term:
State the Relationship
All together now!