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Answer:
B. (n²+n)/2
Step-by-step explanation:
You only need to try n=2 in the answer choices to determine which one gives a result of 3.
A. (2+1)/2 = 3/2 ≠ 3
B. (2² +2)/2 = 3 . . . . correct choice
C. (2² -2)/2 = 1 ≠ 3
D. (2 -1)/2 = 1/2 ≠ 3
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<em>Additional comment</em>
The differences of the sequence 1, 3, 6, 10, ... are increasing, not constant. This means the rule will not be linear, but will be 2nd degree. (Second differences are constant.) This eliminates choices A and D immediately.
