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Date November 2019 Marks available 7 Reference code 19N.1.AHL.TZ0.H_4
Level Additional Higher Level Paper Paper 1 (without calculator) Time zone Time zone 0
Command term Show that Question number H_4 Adapted from N/A

Question

A and B  are acute angles such that  cos A = 2 3 and  sin B = 1 3 .

Show that cos ( 2 A + B ) = 2 2 27 4 5 27 .

Markscheme

attempt to use  cos ( 2 A + B ) = cos 2 A cos B sin 2 A sin B (may be seen later)       M1

attempt to use any double angle formulae (seen anywhere)       M1

attempt to find either sin A or cos B (seen anywhere)       M1

cos A = 2 3 sin A ( = 1 4 9 ) = 5 3        (A1)

sin B = 1 3 cos B ( = 1 1 9 = 8 3 ) = 2 2 3        A1

cos 2 A ( = 2 co s 2 A 1 ) = 1 9        A1

sin 2 A ( = 2 sin A cos A ) = 4 5 9        A1

So   cos ( 2 A + B ) = ( 1 9 ) ( 2 2 3 ) ( 4 5 9 ) ( 1 3 )

= 2 2 27 4 5 27        AG

[7 marks]

Examiners report

[N/A]

Syllabus sections

Topic 3— Geometry and trigonometry » AHL 3.10—Compound angle identities
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Topic 3— Geometry and trigonometry

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