Simplify and evaluate the following constant sums.

MATHEMATICS · Multi-part · A Level · Mathematics · Sequences and series · Sequences and series

Problem

Simplify and evaluate the following constant sums. (i) Find a simplified expression, in terms of mm, for ∑k=1m+57\displaystyle \sum_{k=1}^{m+5} 7, where mm is a positive integer. (ii) Hence determine ∑k=1m+57  −  ∑k=1m−27\displaystyle \sum_{k=1}^{m+5} 7\; - \; \sum_{k=1}^{m-2} 7 and express your answer in the simplest form in terms of mm. (iii) Using your result from part (ii), calculate the value of the expression when m=12m = 12.

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