Question 1083614
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Answer: <font color=red>Choice B) -4</font>
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Explanation:


Pick any term but the first one. Whatever term you picked, subtract off the previous term


Let's say you picked the third term -9. The previous term is -5. Subtract these values:


(term picked) - (previous term) = (-9) - (-5)
(term picked) - (previous term) = -9 + 5
(term picked) - (previous term) = -4


which is the common difference. 


Let's try another selection. Pick the fifth term -17
The previous term is -13

(term picked) - (previous term) = (-17) - (-13)
(term picked) - (previous term) = -17 + 13
(term picked) - (previous term) = -4


we get the same result. This will happen with any selection you make. You can't pick on the first term because there's no known terms before it. 


Note how each term is decreasing by 4 each time. This is another way to see that the common difference is -4

As you can see
second term = (first term) + (common difference) = -1 + (-4) = -5
third term = (second term) + (common difference) = -5 + (-4) = -9
fourth term = (third term) + (common difference) = -9 + (-4) = -13
fifth term = (fourth term) + (common difference) = -13 + (-4) = -17
and so on...

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