Date | May 2019 | Marks available | 1 | Reference code | 19M.1.AHL.TZ2.H_11 |
Level | Additional Higher Level | Paper | Paper 1 | Time zone | Time zone 2 |
Command term | State | Question number | H_11 | Adapted from | N/A |
Question
Consider the functions f and g defined by f(x)=ln|x|, x∈R \ {0}, and g(x)=ln|x+k|, x∈R \ {−k}, where k∈R, k>2.
The graphs of f and g intersect at the point P .
Describe the transformation by which f(x) is transformed to g(x).
State the range of g.
Sketch the graphs of y=f(x) and y=g(x) on the same axes, clearly stating the points of intersection with any axes.
Find the coordinates of P.
The tangent to y=f(x) at P passes through the origin (0, 0).
Determine the value of k.
Markscheme
* This question is from an exam for a previous syllabus, and may contain minor differences in marking or structure.
translation k units to the left (or equivalent) A1
[1 mark]
range is (g(x)∈)R A1
[1 mark]
correct shape of y=f(x) A1
their f(x) translated k units to left (possibly shown by x=−k marked on x-axis) A1
asymptote included and marked as x=−k A1
f(x) intersects x-axis at x=−1, x=1 A1
g(x) intersects x-axis at x=−k−1, x=−k+1 A1
g(x) intersects y-axis at y=lnk A1
Note: Do not penalise candidates if their graphs “cross” as x→±∞.
Note: Do not award FT marks from the candidate’s part (a) to part (c).
[6 marks]
at P ln(x+k)=ln(−x)
attempt to solve x+k=−x (or equivalent) (M1)
x=−k2⇒y=ln(k2) (or y=ln|k2|) A1
P(−k2,lnk2) (or P(−k2,ln|k2|))
[2 marks]
attempt to differentiate ln(−x) or ln|x| (M1)
dydx=1x A1
at P, dydx=−2k A1
recognition that tangent passes through origin ⇒yx=dydx (M1)
ln|k2|−k2=−2k A1
ln(k2)=1 (A1)
⇒k=2e A1
Note: For candidates who explicitly differentiate ln(x) (rather than ln(−x) or ln|x|, award M0A0A1M1A1A1A1.
[7 marks]