The first three terms of an arithmetic progression are $4k$, $k^2$ and $8k$ respectively, with $k$ a non-zero constant.
(a(i))[2]
Determine the value of $k$.
(a(ii))[3]
Determine the sum of the first $20$ terms of the progression.
(b)[5]
Determine the sum to infinity of the progression. Give your answer in the form $\frac{a}{\sqrt{b} - c}$, where $a$, $b$ and $c$ are integers.
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This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Sets up an equation in $k$ from the AP terms” …
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