It is given that f(x) = 2x² – 12x + 10.
- (i)Find the value of a, of b and of c for which f(x) = a(x + b)² + c.[3]
- (ii)Sketch the graph of y = |f(x)| for −1 ≤ x ≤ 7.[4]
- (iii)Find the set of values of k for which the equation |f(x)| = k has 4 distinct roots.[2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2011). The mark or mark type is shown in brackets.
- [B1+B1+B1] (i) a = 2, b = −3, c = −8 or 2(x – 3)² - 8
- [B1] (ii) graph with 3 distinct parts all above and touching x axis
- [B1] (ii) quadratic shape for middle section reflected in x axis
- [B1] (ii) cusp
- [B1] (ii) completely correct
- [M1] (iii) identifies 0 and 8
- [A1] (iii) 0 < k < 8
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