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|=0⇔x+yi+x−yi+|(x+yi)2|=0⇔2x+√(x2+y2)2+(2xy)2=0⇔√(x2+y2)2+(2xy)2=−2x⇔(x2+y2)2+(2xy)2=4x2⇔x4−2x2y2+y4+4x2y2=4x2⇔x4+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:
ρ⋅cis(θ)+ρcis(−θ)+|ρ2⋅cis(2θ)|=0⇔ρ⋅cis(θ)+ρcis(−θ)+ρ2=0⇔ρ(cis(θ)+cis(−θ)+ρ)=0⇔ρ=0∨cis(θ)+cis(−θ)+ρ=0⇔cis(θ)+cis(−θ)=−ρ⇔cos(θ)+sin(θ)i+cos(−θ)+sin(−θ)i=−ρ⇔cos(θ)+cos(θ)=−ρ⇔2cos(θ)=−ρ⇔ρ=−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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