Date | May 2021 | Marks available | 3 | Reference code | 21M.1.AHL.TZ2.12 |
Level | Additional Higher Level | Paper | Paper 1 | Time zone | Time zone 2 |
Command term | Find | Question number | 12 | Adapted from | N/A |
Question
It is given that z1=3 cis(3π4) and z2=2 cis(nπ16), n∈ℤ+.
In parts (a)(i) and (a)(ii), give your answers in the form reiθ, r≥0, −π<θ≤π.
Find the value of z13.
Find the value of (z1z2)4 for n=2.
Find the least value of n such that z1z2∈ℝ+.
Markscheme
z13=27eiπ4 (=27e0.785398… i) A1A1
Note: Award A1 for 27 and A1 for the angle in the correct form.
[2 marks]
(z1z2)4=(8116)eiπ2 (=5.0625e1.57079… i) A1A2
Note: Award A1 for 8116, A2 for the angle in the correct form and A1 for the angle in incorrect form e.g. cisπ2 and/or 5π2. Award A1 if i is given in place of cisπ2.
[3 marks]
z1z2=6 cis (3π4+nπ16) (M1)
=6 cis (12π+nπ16)
12π+nπ=32π (M1)
n=20 A1
[3 marks]