To find the common difference of a recursive formula, we need to find the difference between any two consecutive terms.
In this case, we are given that a4 = an−1 + 2.
This means that the fourth term (a4) is equal to the previous term (an−1) plus 2.
The common difference can be found by subtracting the previous term from the fourth term:
a4 - an−1 = 2.
Since we are given that the fourth term (a4) is equal to the previous term (an−1) plus 2, we can substitute a4 for (an−1 + 2):
(a4) - an−1 = 2.
Simplifying further, we get:
2 = 2.
Since the equation is true, this means that the common difference is 2.
Therefore, the answer is B. 2.