Question

Write the explicit rule.

-21, -51, -81, -111, -141

Answer 1

aₙ = - 30n + 9

Explanation:

You can tell this is an arithmetic sequence, as there is a difference of 30 between each value. Therefore the equation we will use here is aₙ = a₁ + (n - 1)d.

aₙ = a₁ + (n - 1)d

= - 21 + (n - 1) * - 30

= - 21 - 30n + 30

= - 30n + 9

Your solution would be option d. aₙ = - 30n + 9