Easy -1.2 This is a straightforward application of standard summation formulae requiring splitting the sum, applying ∑r² = n(n+1)(2n+1)/6, subtracting n, and factorising. It's routine bookwork with no problem-solving element, though the factorisation adds a small step beyond pure recall.
1 Find $\sum _ { r = 1 } ^ { n } \left( 2 r ^ { 2 } - 1 \right)$, expressing your answer in fully factorised form.
\hfill \mbox{\textit{OCR MEI Further Pure Core 2019 Q1 [4]}}