PROBLEM
Have the function ArithGeo(arr) take the array of numbers stored in arr
and return the string "Arithmetic" if the sequence follows an arithmetic pattern or return "Geometric" if it follows a geometric pattern. If the sequence doesn't follow either pattern return -1.
An arithmetic sequence is one where the difference between each of the
numbers is consistent, where as in a geometric sequence, each term after
the first is multiplied by some constant or common ratio. Arithmetic
example: [2, 4, 6, 8] and Geometric example: [2, 6, 18, 54]. Negative
numbers may be entered as parameters, 0 will not be entered, and no
array will contain all the same elements.