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Date May 2012 Marks available 7 Reference code 12M.2.hl.TZ1.9
Level HL only Paper 2 Time zone TZ1
Command term Find Question number 9 Adapted from N/A

Question

Find the constant term in the expansion of \({\left( {x - \frac{2}{x}} \right)^4}{\left( {{x^2} + \frac{2}{x}} \right)^3}\).

Markscheme

\({\left( {x - \frac{2}{x}} \right)^4} = {x^4} - 8{x^2} + 24 - \frac{{32}}{{{x^2}}} + \frac{{16}}{{{x^4}}}\)     (M1)(A1)

\({\left( {{x^2} + \frac{2}{x}} \right)^3} = {x^6} + 6{x^3} + 12 + \frac{8}{{{x^3}}}\)     (M1)(A1)

 Note: Accept unsimplified or uncalculated coefficients in the constant term

 

\( = 24 \times 12\)     (M1)(A1)

\( = 288\)     A1

[7 marks]

Examiners report

Many correct answers were seen, although most candidates used rather inefficient methods (e.g. expanding the brackets in multiple steps). In a very few cases candidates used the binomial theorem to obtain the answer quickly.

Syllabus sections

Topic 1 - Core: Algebra » 1.3 » The binomial theorem: expansion of \({\left( {a + b} \right)^n}\), \(n \in N\) .
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