Answer: 21, 18, 15
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Explanation:
The notation [tex]a_1[/tex] 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 = [tex]a_1 + d[/tex]
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.
