Write linear function corresponding to the given sequence

Write a linear function that corresponds to the following arithmetic sequence: 8, 1, –6, –13, …
  1. Find the common difference by subtracting two successive terms.
  2. Confirm that the difference is the same between all of the terms.
  3. Identify the first term .
  4. Write the explicit formula.
  5. Simplify the explicit formula.
  6. Write the formula in function notation.