A-LevelMathematicsSeries9709/12 · May/June 2013 · Q25 Marks
Find the coefficient of x² in the expansion of
- (i)(2x - 1/(2x))⁶.[2]
- (ii)(1 + x²)(2x - 1/(2x))⁶.[3]
Mark scheme
Marking points from the official mark scheme (May/June 2013). The mark or mark type is shown in brackets.
- [1] For (i): Correct term for x² in (2x - 1/(2x))⁶ is 15 × (2x)² × (-1/(2x))⁴
- [1] For (i): Coefficient of x² = 60
- [1] For (ii): Constant term (x⁰) from (2x - 1/(2x))⁶ is 20
- [1] For (ii): Considers the constant term from (2x - 1/(2x))⁶ (to multiply by x² from (1+x²)) AND the x² term from (2x - 1/(2x))⁶ (to multiply by 1 from (1+x²))
- [1] For (ii): Final coefficient is 60 - 20 = 40
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