This is the formula of an arithmetic sequence. a n = a 1 + d ( n − 1 ) a n = a 1 + d ( n - 1 ) Substitute in the values of a 1 = 1 a 1 = 1 and d = 3 d = 3 . a n = 1 + ( 3 ) ( n − 1 ) a n = 1 + ( 3 ) ( n - 1 ) Simplify each term. a n = 1 + 3 n − 3 a n = 1 + 3 n - 3 Subtract 3 3 from 1 1 . a n = 3 n − 2
