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Find all complex numbers z such that |z - 3| = |z + i| = |z - 1 - 2i|.

 Apr 8, 2022
 #1
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z = 4i 

 

 

sub in 

 

|4i - 3| = |4i + i| = |4i - 1 - 2i| = |4i -  3| = |5i| = |2i - 1| so

z = i and 5

 Apr 8, 2022
 #2
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 |z - 3| = |z + i| = |z - 1 - 2i|.

 

let z= a+bi


 |a+bi3|=|a+bi+i|=|a+bi12i||(a3)+bi|=|a+(b+1)i|=|(a1)+(b2)i|(a3)2+b2=a2+(b+1)2=(a1)2+(b2)2a26a+9+b2=a2+b2+2b+1=a22a+1+b24b+46a+9=2b+1=2a+14b+46a+8=2b=2a4b+43a+4=b=a2b+2 b=3a+4so3a+4=a2(3a+4)+23a+4=a+6a8+23a+4=5a68a=10a=1.25b=3a+4=3.75+4=0.25z=5+i4

 

 

 

 

 

 

Latex:

|a+bi - 3| = |a+bi + i| = |a+bi - 1 - 2i| \\
 |(a-3)+bi| = |a+(b+1)i| = | (a -1)+(b - 2)i |\\

(a-3)^2+b^2 = a^2+(b+1)^2 = (a-1)^2+(b-2)^2\\
a^2-6a+9+b^2=a^2+b^2+2b+1=a^2-2a+1+b^2-4b+4\\
-6a+9=2b+1=-2a+1-4b+4\\
-6a+8=2b=-2a-4b+4\\
-3a+4=b=-a-2b+2\\~\\
b=-3a+4\\so\\
-3a+4=-a-2(-3a+4)+2\\
-3a+4=-a+6a-8+2\\
-3a+4=5a-6\\
-8a=-10\\
a=1.25\\
b=-3a+4=-3.75+4=0.25\\
z=\frac{5+i}{4}

 Apr 8, 2022
edited by Melody  Apr 8, 2022

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