A-LevelMathematicsSeries9709/12 · Oct/Nov 2017 · Q14 Marks
Find the term independent of x in the expansion of (2x - 1/(4x²))⁹.
- Find the term independent of x in the expansion of (2x - 1/(4x²))⁹.[4]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.
- EITHER: Term is ⁹C₃ × 2⁶ × (-1/4)³ (B1, B1, B1) OE
- OR1: (8x³-1)/(4x²)⁹ = (1/4x²)⁹(8x³-1)⁹ or -(1/4x²)⁹(1-8x³)⁹
- Term is -(1/4)⁹ x ⁹C₆ x 8⁶ (B1, B1, B1) OE
- OR2: Term is 2⁶ x ⁹C₃ x (-1/8)³ (B1, B1, B1) OE
- Selected term, which must be independent of x = -84 (B1)
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