The sum can be rewritten in the standard form

MATHEMATICS · Single correct · A Level · Mathematics · Sequences and series · Sequences and series

Problem

The sum ∑k=4n+3(10−k)\displaystyle \sum_{k=4}^{n+3}(10 - k) can be rewritten in the standard form ∑j=1n(A+(j−1)D)\displaystyle \sum_{j=1}^{n} \bigl(A + (j-1)D\bigr). Which pair (A,D)(A,D) is correct? (a) (7, −1)(7,\,-1) (b) (10, −1)(10,\,-1) (c) (6, −1)(6,\,-1) (d) (6, 1)(6,\,1)

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