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Date May Specimen paper Marks available 3 Reference code SPM.1.SL.TZ0.5
Level Standard Level Paper Paper 1 (without calculator) Time zone Time zone 0
Command term Find Question number 5 Adapted from N/A

Question

The functions f and g are defined such that  f ( x ) = x + 3 4 and  g ( x ) = 8 x + 5 .

Show that ( g f ) ( x ) = 2 x + 11 .

[2]
a.

Given that ( g f ) 1 ( a ) = 4 , find the value of a .

[3]
b.

Markscheme

attempt to form composition       M1

correct substitution  g ( x + 3 4 ) = 8 ( x + 3 4 ) + 5     A1

( g f ) ( x ) = 2 x + 11      AG

[2 marks]

a.

attempt to substitute 4 (seen anywhere)     (M1)

correct equation  a = 2 × 4 + 11       (A1)

a = 19     A1

[3 marks]

b.

Examiners report

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

Syllabus sections

Topic 2—Functions » SL 2.5—Composite functions, identity, finding inverse
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Topic 2—Functions

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