The function f(x) = x³ + x² + ax + b is divisible by x - 3 and leaves a remainder of 20 when divided by x + 1.
- (i)Show that b = 6 and find the value of a.[4]
- (ii)Using your value of a and taking b as 6, find the non-integer roots of the equation f(x) = 0 in the form p ± √q, where p and q are integers.[5]
Mark scheme
Marking points from the official mark scheme (May/June 2013). The mark or mark type is shown in brackets.
- [1] (i) f(3) = (27 + 9 + 3a + b) = 0 or 3a + b = -36
- [1] (i) f(-1) = (-1 + 1 – a + b) = 20 or -a + b = 20
- [1] (i) Solve equations
- [1] (i) a = -14, b = 6
- [1] (ii) Find quadratic factor
- [1] (ii) x² - 4x - 2
- [1] (ii) Use quadratic formula or completing square on relevant 3 term quadratic
- [1] (ii) (-4 ± √16+8) / 2 or better
- [1] (ii) 2 ± √6 isw
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