Question

Find the 20th term of the arithmetic sequence whose common difference is d=3 and whose first term is a₁ = 4.

Answer 1

The general formula for an arithmetic sequence is given by

`a_n=a_1+d(n-1)`

where

a_1=4

d=3

substitute

`\begin{gathered} a_n=4+3(n-1) \\ a_n=4+3n-3 \\ a_n=3n+1 \end{gathered}`

so

For n=20

substitute

`\begin{gathered} a_(20)=3(20)+1 \\ a_(20)=61 \end{gathered}`

The answer is 61