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Express the quotient in polar form with principal argument −π<θ≤π.

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TOPIC 01

2024 JM02

Arguments subtract under division.

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01 / Standard#Your turn

Express the quotient in polar form with principal argument −π<θ≤π.

z=3+i1+iz=\frac{\sqrt3+i}{1+i}

Official paper · jm02-2024 · 4(a)(i) · PDF 6

Official original and suggested answers ↗ · Suggested answer PDF page 10

Skills and prerequisite lessons

Working and explanation

BUILD THE REASONING

Hint 1
Find modulus and argument of numerator and denominator.
Hint 2
Divide moduli and subtract arguments.
Worked solution
  1. Write the two numbers in polar form.

    3+i=2cis⁡(π/6),1+i=2cis⁡(π/4)\sqrt3+i=2\operatorname{cis}(\pi/6),\quad1+i=\sqrt2\operatorname{cis}(\pi/4)
  2. The resulting argument is already principal.

    z=2[cos⁡(−π/12)+isin⁡(−π/12)]z=\sqrt2[\cos(-\pi/12)+i\sin(-\pi/12)]

Modulus √2, principal argument −π/12.

Checks and common pitfalls: Arguments subtract under division.

Reasoning checklist · self / teacher assessment
  • Teaching assessment checklist, independently authored. Use the original paper for official marks.
  • Write the two numbers in polar form.
    3+i=2cis⁡(π/6),1+i=2cis⁡(π/4)\sqrt3+i=2\operatorname{cis}(\pi/6),\quad1+i=\sqrt2\operatorname{cis}(\pi/4)
  • The resulting argument is already principal.
    z=2[cos⁡(−π/12)+isin⁡(−π/12)]z=\sqrt2[\cos(-\pi/12)+i\sin(-\pi/12)]

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Curriculum and source notes ↗