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Date May Example question Marks available 2 Reference code EXM.1.AHL.TZ0.29
Level Additional Higher Level Paper Paper 1 Time zone Time zone 0
Command term Show that Question number 29 Adapted from N/A

Question

Let M ( a b b a ) where a and b are non-zero real numbers.

Show that M is non-singular.

[2]
a.

 Calculate M2.

[2]
b.

 Show that det(M2) is positive.

[2]
c.

Markscheme

finding det M = a 2 + b 2          A1

a 2 + b 2 > 0 , therefore M is non-singular or equivalent statement        R1

[2 marks]

a.

M2 = ( a b b a ) ( a b b a ) = ( a 2 b 2 2 a b 2 a b a 2 b 2 )            M1A1

[2 marks]

b.

EITHER          

det(M2) = ( a 2 b 2 ) ( a 2 b 2 ) + ( 2 a b ) ( 2 a b )                       A1

det(M2) = ( a 2 b 2 ) 2 + ( 2 a b ) 2       ( = ( a 2 + b 2 ) 2 )

since the first term is non-negative and the second is positive          R1

therefore det(M2) > 0          

Note: Do not penalise first term stated as positive.          

OR          

det(M2) = (det M)2              A1

since det M is positive so too is det (M2)       R1

[2 marks]

c.

Examiners report

[N/A]
a.
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b.
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c.

Syllabus sections

Topic 1—Number and algebra » AHL 1.14—Introduction to matrices
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Topic 1—Number and algebra

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