Eric Nicholas K's answer to Alina's Junior College 2 H2 Maths Singapore question.

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Eric Nicholas K
Eric Nicholas K's answer
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I highly doubt that a question at the JC level will appear like that. The formulas for the expansions should be given as part of the question unless there is an alternative method for it. I don't recall any special expansion technique for the summation of r (r + 1) though.