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Date May 2016 Marks available 2 Reference code 16M.1.sl.TZ1.1
Level SL only Paper 1 Time zone TZ1
Command term Find Question number 1 Adapted from N/A

Question

Let \(f(x) = 8x + 3\) and \(g(x) = 4x\), for \(x \in \mathbb{R}\).

Write down \(g(2)\).

[1]
a.

Find \((f \circ g)(x)\).

[2]
b.

Find \({f^{ - 1}}(x)\).

[2]
c.

Markscheme

\(g(2) = 8\)    A1     N1

[1 mark]

a.

attempt to form composite (in any order)     (M1)

eg\(\,\,\,\,\,\)\(f(4x),{\text{ }}4 \times (8x + 3)\)

\((f \circ g)(x) = 32x + 3\)     A1     N2

[2 marks]

b.

interchanging \(x\) and \(y\) (may be seen at any time)     (M1)

eg\(\,\,\,\,\,\)\(x = 8y + 3\)

\({f^{ - 1}}(x) = \frac{{x - 3}}{8}\,\,\,\,\,\left( {{\text{accept }}\frac{{x - 3}}{8},{\text{ }}y = \frac{{x - 3}}{8}} \right)\)     A1     N2

[2 marks]

c.

Examiners report

This question was successfully answered by most candidates. The inverse notation was sometimes mistakenly interpreted as derivative or reciprocal.

a.

This question was successfully answered by most candidates. The inverse notation was sometimes mistakenly interpreted as derivative or reciprocal.

b.

This question was successfully answered by most candidates. The inverse notation was sometimes mistakenly interpreted as derivative or reciprocal.

c.

Syllabus sections

Topic 2 - Functions and equations » 2.1 » Concept of function \(f:x \mapsto f\left( x \right)\) .
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