Sequences
2 marks · NormalExplain why the sequence 1, 2, 4, 7, 11, ... is not an arithmetic sequence.
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The difference between terms is not constant.
Also accept: The difference between terms keeps changing; in an arithmetic sequence, it should be the same.
Common mistakes: Just stating 'not arithmetic' with no reason.
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Marking points
B1 · 1 mark · States the difference between terms is not constant (or equivalent).
B2 · 1 mark · Identifies that in an arithmetic sequence, the difference between consecutive terms is always the same.
Worked solution
Find the differences:
The differences are not equal, so this is not an arithmetic sequence.