Question

Find a8 when a1= 9, d = 4 of the arithmetic sequence whose first term is a1 and common difference is d.

Answer 1

General Arithmetic Terms

$\displaystyle \large{a_n = a_1 + (n - 1)d}$

We want to find a8; we know:

• a1 = 9
• d = 4

Substitute in the formula.

$\displaystyle \large{a_n = 9 + (n - 1)4} \\ \displaystyle \large{a_n = 9 + 4n - 4} \\ \displaystyle \large{a_n = 4n + 5}$

To find a8, substitute n = 8

$\displaystyle \large{a_8= 4(8) + 5} \\ \displaystyle \large{a_8= 32 + 5} \\ \displaystyle \large{a_8= 37}$

Hence, the 8th term of sequence is 37