Find the first term the common difference and give a recursi

Find the first term, the common difference, and give a recursive formula for the arithmetic sequence.

7th term is 4; 13th term is 16

7th term is 4; 13th term is 16

nth term : an = a1 + (n-1)d

4 = a1+ (7-1)d -----> 4 = a1+6d

16 = a1 +(13-1)d ---> 16 = a1 +12d

12 = 6d ---> d = 2

a1 = 4 -6d = 4 -12 = -8

So, a1 = -8 ; d = 2

an = -8 +(n-1)2 = -8 +2n -2 = 2n - 10