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Date May 2019 Marks available 3 Reference code 19M.2.AHL.TZ1.H_6
Level Additional Higher Level Paper Paper 2 Time zone Time zone 1
Command term Find and Hence or otherwise Question number H_6 Adapted from N/A

Question

Let z=a+bi, abR+ and let argz=θ.

Show the points represented by z and z2a on the following Argand diagram.

[1]
a.

Find an expression in terms of θ for arg(z2a).

[1]
b.i.

Find an expression in terms of θ for arg(zz2a).

[2]
b.ii.

Hence or otherwise find the value of θ for which Re(zz2a)=0.

[3]
c.

Markscheme

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

      A1

Note: Award A1 for z in first quadrant and z2a its reflection in the y-axis.

[1 mark]

a.

πθ (or any equivalent)     A1

[1 mark]

b.i.

arg(zz2a)=arg(z)arg(z2a)     (M1)

=2θπ (or any equivalent)       A1

[2 marks]

b.ii.

METHOD 1

if Re(zz2a)=0 then 2θπ=nπ2, (n odd)     (M1)

π<2θπ<0n=1

2θπ=π2     (A1)

θ=π4       A1

 

METHOD 2

a+bia+bi=b2a22abia2+b2      M1

Re(zz2a)=0b2a2=0

b=a       A1

θ=π4       A1

Note: Accept any equivalent, eg θ=7π4.

 

 

[3 marks]

c.

Examiners report

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

Syllabus sections

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

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