Simplify for a positive integer .

MATHEMATICS · Single correct · CBSE · Mathematics · Sequences and Series · Sequences and Series

Problem

Simplify ∑k=1n(5k+7)  −  5∑k=1nk\displaystyle \sum_{k=1}^{n} (5k + 7)\; - \; 5\sum_{k=1}^{n} k for a positive integer nn. (a) 12n12n (b) 7n7n (c) 7(n+1)7(n+1) (d) 7n2\dfrac{7n}{2}

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