The polynomial p(x) is defined by p(x) = ax³ – ax² – 15x + 18, where a is a constant. It is given that (x+2) is a factor of p(x).
- (a)Find the value of a.[2]
- (b)Hence factorise p(x) completely.[3]
- (c)Solve the equation p(cosec²θ) = 0 for -90° < θ < 90°.[3]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2024). The mark or mark type is shown in brackets.
- [M1] Substitute x = −2, equate to zero and attempt solution
- [A1] Obtain a = 4
- [M1] Divide by x + 2 at least as far as k₁x² + k₂x
- [A1] Obtain 4x² - 12x + 9
- [A1] Obtain (x + 2)(2x - 3)² or equivalent with integer coefficients only
- [M1] Equate sin²θ to appropriate value from factorised form and attempt solution
- [A1] Obtain 54.7
- [A1] Obtain -54.7
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