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Date May 2017 Marks available 3 Reference code 17M.2.sl.TZ2.6
Level SL only Paper 2 Time zone TZ2
Command term Sketch Question number 6 Adapted from N/A

Question

Let f(x)=x21 and g(x)=x22, for xR.

Show that (fg)(x)=x44x2+3.

[2]
a.

On the following grid, sketch the graph of (fg)(x), for 0.

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

[3]
b.

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

[3]
c.

Markscheme

attempt to form composite in either order     (M1)

eg\,\,\,\,\,f({x^2} - 2),{\text{ }}{({x^2} - 1)^2} - 2

({x^4} - 4{x^2} + 4) - 1     A1

(f \circ 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,{\text{ }}1.41421,{\text{ }}y =  - 1,{\text{ }}3

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

eg\,\,\,\,\, - 1 < k \leqslant 3,{\text{ }}\left] { - 1,{\text{ 3}}} \right],{\text{ }}( - 1,{\text{ }}3]

[3 marks]

c.

Examiners report

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b.
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c.

Syllabus sections

Topic 2 - Functions and equations » 2.7 » Solving equations, both graphically and analytically.
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