Using an appropriate quadratic factorisation, find the first three terms in the binomial expansion of (9x²+12x+4)⁵, in ascending powers of x. You must simplify your coefficients.
- (a)Using an appropriate quadratic factorisation, find the first three terms in the binomial expansion of (9x²+12x+4)⁵, in ascending powers of x. You must simplify your coefficients.[4]
- (b)Find the term independent of x in the expansion of (6/x² + x/2)¹².[2]
Mark scheme
Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.
- [M2] M1 for (3x + 2)² soi
- [A2] A1 for any two terms correct or 2¹⁰ + 10(2⁹)(3x) + 45(2⁸)(3x)² or for 3 correct terms seen but not summed e.g. a list
- After M2 A0, allow SC1 for an answer of 59 049x¹⁰ + 393660x⁹ + 1180980x⁸
- [A1] 1024 + 15360x + 103 680x²
- [M1] for C(6/x²)^(12-r)(x/2)^r soi
- [A1] 51 963 120
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