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Date May 2017 Marks available 3 Reference code 17M.2.SL.TZ2.S_6
Level Standard Level Paper Paper 2 Time zone Time zone 2
Command term Sketch Question number S_6 Adapted from N/A

Question

Let f ( x ) = x 2 1 and g ( x ) = x 2 2 , for x R .

Show that ( f g ) ( x ) = x 4 4 x 2 + 3 .

[2]
a.

On the following grid, sketch the graph of ( f g ) ( x ) , for 0 x 2.25 .

M17/5/MATME/SP2/ENG/TZ2/06.b

[3]
b.

The equation ( f g ) ( x ) = k has exactly two solutions, for 0 x 2.25 . Find the possible values of k .

[3]
c.

Markscheme

* This question is from an exam for a previous syllabus, and may contain minor differences in marking or structure.

attempt to form composite in either order     (M1)

eg f ( x 2 2 ) ,   ( x 2 1 ) 2 2

( x 4 4 x 2 + 4 ) 1     A1

( f g ) ( x ) = x 4 4 x 2 + 3     AG     N0

[2 marks]

a.

M17/5/MATME/SP2/ENG/TZ2/06.b/M    A1

A1A1     N3

 

Note:     Award A1 for approximately correct shape which changes from concave down to concave up. Only if this A1 is awarded, award the following:

A1 for left hand endpoint in circle and right hand endpoint in oval,

A1 for minimum in oval.

 

[3 marks]

b.

evidence of identifying max/min as relevant points     (M1)

eg x = 0 ,   1.41421 ,   y = 1 ,   3

correct interval (inclusion/exclusion of endpoints must be correct)     A2     N3

eg 1 < k 3 ,   ] 1 ,  3 ] ,   ( 1 ,   3 ]

[3 marks]

c.

Examiners report

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

Syllabus sections

Topic 2—Functions » SL 2.2—Functions, notation domain, range and inverse as reflection
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