Mathematics 9709 · AS & A Level · Series

Series — practice question

The formula for the $n$th term of an arithmetic progression is $\frac{1}{2}(3n - 15)$.
(main)[5]

Find the value of $n$ at which the sum of the first $n$ terms is 84.

Worked solution & mark scheme

This 5-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Identify the first two terms as $-6$ and $-4.5$.” …

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