Mathematics 9709 · AS & A Level · Series

Series — practice question

The progression has $20$, $k$ and $k-5$ as its first, second and third terms respectively.
(a)[2]

Since the progression is arithmetic, determine the 30th term.

(b)[4]

If the progression is geometric instead, determine the sum to infinity.

Worked solution & mark scheme

This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Substitute $d=-5$ into $u_{30}=20+(30-1)\times d$.” …

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