(a)[2]
Determine the value of the constant $a$.
(b)[3]
Hence determine the coefficient of $x^3$ in the expansion of $(3 + ax)^6(1 - 2x)$.
Mathematics 9709 · AS & A Level · Series
Series — practice question
Within the expansion of $(3 + ax)^6$, the coefficient of $x^3$ is $160$.
Worked solution & mark scheme
This 5-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Sets up equation $20\times27\times a^3=160$ (or equivalent)” …
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