The first term of an arithmetic sequence is -5, and the tenth term is 13.?

Question

what is the common difference?

Answer 1

now = difference(last) + initial

f(n) = x(n - 1) + i

n=1:

-5 = x(1 - 1) + i

i = -5

n=10:

13 = x(10 - 1) - 5

13 = x(9) - 5

9x = 18

x = 2