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Date May 2019 Marks available 6 Reference code 19M.1.AHL.TZ2.H_11
Level Additional Higher Level Paper Paper 1 Time zone Time zone 2
Command term Sketch and 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 ) .

[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 = k 1 , x = k + 1        A1

g ( x )  intersects  y -axis at  y = ln k        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 = k 2 y = ln ( k 2 )   (or  y = ln | k 2 | )       A1

P ( k 2 , ln k 2 )   (or P ( k 2 , ln | k 2 | ) )

[2 marks]

d.

attempt to differentiate  ln ( x ) or  ln | x |        (M1)

d y d x = 1 x        A1

at P,  d y d x = 2 k        A1

recognition that tangent passes through origin  y x = d y d x        (M1)

ln | k 2 | k 2 = 2 k        A1

ln ( k 2 ) = 1        (A1)

k = 2 e        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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