Mathematics 9709 · AS & A Level · Series

Series — practice question

The coefficient attached to $x^3$ in the expansion of $(1 + kx)(1 - 2x)^5$ is $20$.
(main)[4]

Find the value for the constant $k$.

Worked solution & mark scheme

This 4-mark question has a full step-by-step worked solution and mark scheme. One marking point: “The coefficient of $x^3$ in $(1-2x)^5$ is $-80$” …

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