Just working through my FP1 book and have got stuck on a question.(adsbygoogle = window.adsbygoogle || []).push({});

Use the identity [itex](r+1)^3 - r^3 \equiv3r^2 + 3r + 1[/itex]

to find [itex]\sum\limits_{r = 1}^n r(r+1)[/itex]

I've tried using the method of differences to get [itex]n^3 + 3n^2 + 3n[/itex], but cant see how to get it back into its original form, not sure how the identity corresponds to r(r+1).

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# Homework Help: Using an identity to find the sum to n terms of a series

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