Question

Which one is a rule for the nth term of an arithmetic sequence with a8 = 56 and d = 5?

Answer 1

An for arithmetic sequence, an = a + (n - 1)d
a8 = a + (8 - 1) x 5 = a + 7 x 5 = a + 35 = 56
a = 56 - 35 = 21

Therefore, an = 21 + (n - 1) x 5 = 21 + 5n - 5 = 16 + 5n
an = 16 + 5n