Question

Find a12 in the arithmetic sequence if a1 = 20 and d = 2

Answer 1

The value of a
`_(12)` is 42

Explanation:

The explicit formula of the arithmetic sequence is a
`_(n)` = a + (n - 1)d, where

• a is the first term

• d is the common difference

• n is the position of the term in the sequence

∵ a
`_(1)` = 20 ⇒ first term

∴ a = 20

∵ d = 2 ⇒ common difference

∵ We need to find a
`_(12)`

∴ n = 12

→ Substitute them in the formula above

∵ a
`_(12)` = 20 + (12 - 1)(2)

∴ a
`_(12)` = 20 + (11)(2)

∴ a
`_(12)` = 20 + 22

∴ a
`_(12)` = 42

∴ The value of a
`_(12)` is 42