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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 + b i , a b R + and let  arg z = θ .

Show the points represented by z and z 2 a on the following Argand diagram.

[1]
a.

Find an expression in terms of θ for  arg ( z 2 a ) .

[1]
b.i.

Find an expression in terms of θ for arg ( z z 2 a ) .

[2]
b.ii.

Hence or otherwise find the value of θ for which  Re ( z z 2 a ) = 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 z 2 a its reflection in the y -axis.

[1 mark]

a.

π θ  (or any equivalent)     A1

[1 mark]

b.i.

arg ( z z 2 a ) = arg ( z ) arg ( z 2 a )      (M1)

= 2 θ π  (or any equivalent)       A1

[2 marks]

b.ii.

METHOD 1

if  Re ( z z 2 a ) = 0 then  2 θ π = n π 2 , ( n odd)     (M1)

π < 2 θ π < 0 n = 1

2 θ π = π 2      (A1)

θ = π 4        A1

 

METHOD 2

a + b i a + b i = b 2 a 2 2 a b i a 2 + b 2       M1

Re ( z z 2 a ) = 0 b 2 a 2 = 0

b = a        A1

θ = π 4        A1

Note: Accept any equivalent, eg  θ = 7 π 4 .

 

 

[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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