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Date May 2017 Marks available 3 Reference code 17M.1.AHL.TZ1.H_2
Level Additional Higher Level Paper Paper 1 (without calculator) Time zone Time zone 1
Command term Write down Question number H_2 Adapted from N/A

Question

Consider the complex numbers z 1 = 1 + 3 i,  z 2 = 1 + i and w = z 1 z 2 .

By expressing z 1 and z 2 in modulus-argument form write down the modulus of w ;

[3]
a.i.

By expressing z 1 and z 2 in modulus-argument form write down the argument of w .

[1]
a.ii.

Find the smallest positive integer value of n , such that w n is a real number.

[2]
b.

Markscheme

z 1 = 2 cis ( π 3 ) and z 2 = 2 cis ( π 4 )     A1A1

 

Note:     Award A1A0 for correct moduli and arguments found, but not written in mod-arg form.

 

| w | = 2     A1

[3 marks]

a.i.

z 1 = 2 cis ( π 3 ) and z 2 = 2 cis ( π 4 )     A1A1

 

Note:     Award A1A0 for correct moduli and arguments found, but not written in mod-arg form.

 

arg w = π 12     A1

 

Notes:     Allow FT from incorrect answers for z 1 and z 2 in modulus-argument form.

 

[1 mark]

a.ii.

EITHER

sin ( π n 12 ) = 0     (M1)

OR

arg ( w n ) = π     (M1)

n π 12 = π

THEN

n = 12     A1

[2 marks]

b.

Examiners report

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

Syllabus sections

Topic 1—Number and algebra » AHL 1.13—Polar and Euler form
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