How do I solve this problem?

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Explanation:

The notation refers to the first term. So the first term is 21.

The d = -3 is the common difference. It's the value we add onto any given term to get the next following term.

We can say:

second term = (first term) + (common difference)

second term =

second term = 21 + (-3)

second term = 18

Through similar steps, you should find that the third term is 15, the fourth is 12, and so on. Each time we decrease by 3.

The arithmetic sequence would be: 21, 18, 15, 12, 9, ...

The first three terms are 21, 18, and 15.

answer: my brother can figure it out, imma go get him so i can answer : ) edit: my brother is sleeping, sorry man

step-by-step explanation: