Sunday, 27 May 2018

calculus - What does the group of the geometric images of z, such that z+overlinez+|z2|=0 define?




What does the group of the geometric images of z, such that
z+¯z+|z2|=0 define?



A) A circumference of center (0,-1) and radius 1.




B) Two lines, of equations y=x+2 and y=x.



C)A circumference of center (1,0) and radius 1.



D)A circumference of center (-1,0) and radius 1.




I tried to simplify the expression:




z+¯z+|z2|=0x+yi+xyi+|(x+yi)2|=02x+(x2+y2)2+(2xy)2=0(x2+y2)2+(2xy)2=2x(x2+y2)2+(2xy)2=4x2x42x2y2+y4+4x2y2=4x2x4+y4+2x2y2=4x2???



How do I continue from here?




I have also been thinking that if the sum of those three numbers is zero then they could be the vertices of a triangle. I rewrote the expression:



ρcis(θ)+ρcis(θ)+|ρ2cis(2θ)|=0ρcis(θ)+ρcis(θ)+ρ2=0ρ(cis(θ)+cis(θ)+ρ)=0ρ=0cis(θ)+cis(θ)+ρ=0cis(θ)+cis(θ)=ρcos(θ)+sin(θ)i+cos(θ)+sin(θ)i=ρcos(θ)+cos(θ)=ρ2cos(θ)=ρρ=2cos(θ)



This means that ρ will be between 0 and 2. If |z2|=ρ2=ρ2cis(0), then one of the vertices is 4.



But what do I do next? How do I solve this?


Answer



That solution is very laboured: |z2|=x2+y2 so the curve's equation is
x2+y2+2x=0
or

(x+1)2+y2=1.
I'm sure you can identify the curve now.


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