Question

Given the arithmetic sequence of 21,
6, 9, 24,
find an explicit rule for the nth term.

Answer 1

Explanation:

The sequence you gave is not arithmetic. I'm assuming the sequence is

21, 6, -9, -24.

d is the common difference between adjacent terms.

a₂ = a₁ + d

6 = 21 + d

d = -15

nth term = a₁ + (n-1)d = 21 - (n-1)15