The curve C has equation y = (2x² + kx)/(x+1), where k is a constant. Find the set of values of k for which C has no stationary points. For the case k = 4, find the equations of the asymptotes of C and sketch C, indicating the coordinates of the points where C intersects the coordinate axes.
- (a)Find the set of values of k for which C has no stationary points.[5]
- (b)For the case k = 4, find the equations of the asymptotes of C and sketch C, indicating the coordinates of the points where C intersects the coordinate axes.[6]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2015). The mark or mark type is shown in brackets.
- [M1] (a) y' = (x+1)(4x+k) - (2x²+kx) / (x+1)² = 0
- [A1] (a) ⇒ 2x² + 4x + k = 0
- [M1] (a) B² − 4AC < 0
- [A1] (a) ⇒ 16 − 8k < 0
- [A1] (a) ⇒ k > 2 for no stationary points.
- [B1] (b) Vertical asymptote: x = -1
- [M1] (b) Oblique asymptote: y = 2x+2 - 2/(x+1)
- [A1] (b) ⇒ y = 2x + 2
- [B1] (b) Axes and asymptotes (sketch)
- [B1] (b) Each branch (sketch)
- [B1] (b) Intercepts (sketch)
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