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Date May 2021 Marks available 5 Reference code 21M.2.AHL.TZ2.8
Level Additional Higher Level Paper Paper 2 Time zone Time zone 2
Command term Show that Question number 8 Adapted from N/A

Question

Consider z=cosθ+isinθ where z, z1.

Show that Re1+z1-z=0.

Markscheme

1+z1-z=1+cosθ+isinθ1-cosθ-isinθ

attempt to use the complex conjugate of their denominator           M1

=1+cosθ+isinθ1-cosθ+isinθ1-cosθ-isinθ1-cosθ+isinθ            A1

Re1+z1-z=1-cos2θ-sin2θ1-cosθ2+sin2θ  =1-cos2θ-sin2θ2-2cosθ          M1A1


Note:
Award M1 for expanding the numerator and A1 for a correct numerator. Condone either an incorrect denominator or the absence of a denominator.


using cos2θ+sin2θ=1 to simplify the numerator           (M1)

Re1+z1-z=0            AG

 

[5 marks]

Examiners report

[N/A]

Syllabus sections

Topic 1—Number and algebra » AHL 1.12—Complex numbers – Cartesian form and Argand diag
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Topic 1—Number and algebra

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