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Date May Specimen paper Marks available 3 Reference code SPM.1.AHL.TZ0.9
Level Additional Higher Level Paper Paper 1 (without calculator) Time zone Time zone 0
Command term Find Question number 9 Adapted from N/A

Question

The function ff is defined by f(x)=e2x6ex+5,xR,xa. The graph of y=f(x) is shown in the following diagram.

Find the largest value of a such that f has an inverse function.

[3]
a.

For this value of a, find an expression for f1(x), stating its domain.

[5]
b.

Markscheme

attempt to differentiate and set equal to zero       M1

f(x)=2e2x6ex=2ex(ex3)=0       A1

minimum at x=ln3

a=ln3       A1

[3 marks]

a.

Note: Interchanging x and y can be done at any stage.

y=(ex3)24     (M1)

ex3=±y+4     A1

as xln3x=ln(3y+4)       R1

so f1(x)=ln(3x+4)    A1

domain of f1 is xR4x<5    A1

[5 marks]

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Topic 2—Functions » AHL 2.14—Odd and even functions, self-inverse, inverse and domain restriction
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Topic 2—Functions

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