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=cos θ+i sin θ where z∈ℂ, z≠1.
Show that Re(1+z1-z)=0.
Markscheme
1+z1-z=1+cos θ+i sin θ1-cos θ-i sin θ
attempt to use the complex conjugate of their denominator M1
=(1+cos θ+i sin θ)(1-cos θ+i sin θ)(1-cos θ-i sin θ)(1-cos θ+i sin θ) A1
Re(1+z1-z)=1-cos2 θ-sin2 θ(1-cos θ)2+sin2 θ (=1-cos2 θ-sin2 θ2-2 cos θ) 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 cos2 θ+sin2 θ=1 to simplify the numerator (M1)
Re(1+z1-z)=0 AG
[5 marks]