Question

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

A.an = 16 − 5n
B.an = 26 + 5n
C.an = 26 − 5n
D.an = 16 + 5n

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