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Date May 2018 Marks available 2 Reference code 18M.2.AHL.TZ2.H_1
Level Additional Higher Level Paper Paper 2 Time zone Time zone 2
Command term Express Question number H_1 Adapted from N/A

Question

Consider the complex number  z = 2 + 7 i 6 + 2 i .

Express  z in the form  a + i b , where  a , b Q .

[2]
a.

Find the exact value of the modulus of z .

[2]
b.

Find the argument of z , giving your answer to 4 decimal places.

[2]
c.

Markscheme

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

z = ( 2 + 7 i ) ( 6 + 2 i ) × ( 6 2 i ) ( 6 2 i )      (M1)

= 26 + 38 i 40 = ( 13 + 19 i 20 = 0.65 + 0.95 i )      A1

[2 marks]

a.

attempt to use | z | = a 2 + b 2     (M1)

| z | = 53 40 ( = 530 20 )  or equivalent      A1

Note: A1 is only awarded for the correct exact value.

[2 marks]

b.

EITHER

arg  z = arg(2 + 7i) − arg(6 + 2i)      (M1)

OR

arg  z = arctan ( 19 13 )         (M1)

THEN

arg  z = 0.9707 (radians) (= 55.6197 degrees)     A1

Note: Only award the last A1 if 4 decimal places are given.

[2 marks]

c.

Examiners report

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