Final answer:
To find the ninth term of an arithmetic sequence, subtract the third term from the seventeenth term to find the common difference. Then, add the common difference eight times to the third term to find the ninth term.
Step-by-step explanation:
To find the ninth term of an arithmetic sequence, we need to determine the common difference between the terms. The common difference can be found by subtracting the third term from the seventeenth term. So, the common difference is -66 - 4 = -70.
Now that we know the common difference, we can find the ninth term by adding the common difference (−70) eight times to the third term (4). Ninth term = 4 + 8 * (-70) = -556.