Skip to main content

2023 AMC 12A Problem 14

Problem 14 of 25IntermediateAlgebra

How many complex numbers satisfy the equation z5=z‾,z^5=\overline{z}, where z‾\overline{z} is the conjugate of the complex number z?z?

Answer choices

Show solution

Solution

Taking magnitudes gives ∣z∣5=∣z∣,|z|^5=|z|, so ∣z∣=0|z|=0 or ∣z∣=1.|z|=1. The value z=0z=0 works, giving one solution. If ∣z∣=1,|z|=1, multiply the equation by zz to get z6=zz‾=∣z∣2=1.z^6=z\overline{z}=|z|^2=1. This has 66 distinct roots, all of modulus 1.1. Altogether there are 1+6=71+6=7 solutions. Thus, the correct answer is E.
AoPS wiki

Tagged: complex number · roots of unity

More practice