Mathematics 9709 · AS & A Level · Series

Series — practice question

(i)[1]

Find the coefficient of $x^8$ in the expansion of $(x + 3x^2)^4$.

(ii)[3]

Find the coefficient of $x^8$ in the expansion of $(x + 3x^2)^5$.

(iii)[4]

Hence find the coefficient of $x^8$ that appears in the expansion of $[1 + (x + 3x^2)]^5$.

Worked solution & mark scheme

This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Coefficient $81(x^8)” …