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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|, xR \ {0}, and g(x)=ln|x+k|xR \ {k}, where kRk>2.

The graphs of f and g intersect at the point P .

Describe the transformation by which f(x) is transformed to g(x).

[1]
a.

State the range of g.

[1]
b.

Sketch the graphs of y=f(x) and y=g(x) on the same axes, clearly stating the points of intersection with any axes.

[6]
c.

Find the coordinates of P.

[2]
d.

The tangent to y=f(x) at P passes through the origin (0, 0).

Determine the value of k.

[7]
e.

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]

a.

range is (g(x))R     A1

[1 mark]

b.

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=k1, 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]

c.

at P  ln(x+k)=ln(x)

attempt to solve x+k=x (or equivalent)       (M1)

x=k2y=ln(k2)  (or y=ln|k2|)       A1

P(k2,lnk2)  (or P(k2,ln|k2|))

[2 marks]

d.

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]

e.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.
[N/A]
d.
[N/A]
e.

Syllabus sections

Topic 2—Functions » AHL 2.8—Transformations of graphs, composite transformations
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