Question

What is the explicit formula for this sequence ? -9,-3,3,9,15,...

Answer 1

`B.\ \ a_n=(-9)+(n-1)6`

Explanation:

`a_1=-9\,,\ a_2=-3\,,\ a_3=3\,,\ a_4=9\,,\ a_5=15...\implies d=6`

{-9-(-3)=6 and 3-(-3)=6 and 9-3=6 and 15-9=6}

An arithmetic sequence is:
`a_n=a_1+(n-1)d`

`a_1=-9\quad and\quad d=6`

`a_n=-9+(n-1)\cdot6`