if arithmetic, then there is a common difference
if geometric, then there is a common ratio
to find the common ratio or difference
if you subtract successive terms from each other, they should have the same result if it is aritmetic
if you divide successive terms by each other, they should have the same result if it is geometric
2,3 and 5
3-2=1
5-3=2
2≠1
not aritmetic
3/2=1.5
5/3=1.66666
1.5≠1.6666
not geometric
she is wrong
