Let z1=x1+iy1 and z2=x2+iy2
Given ∣z1−1∣=Re(z1)
⇒(x1−1)2+y12=x12
⇒y12−2x1+1=0..............(1)
∣z2−1∣=Re(z2)
⇒(x2−1)2+y22=x22
⇒y22−2x2+1=0...........(2)
Subtracting equation (2) from equation (1), we get
y12−y22−2(x1−x2)=0
⇒(y1−y2)(y1+y2)=2(x1−x2)
⇒y1+y2=2(y1−y2x1−x2)............(3)
Also given, arg(z1−z2)=6π
⇒tan−1(x1−x2y1−y2)=6π
⇒x1−x2y1−y2=31.........(4)
Putting equation (4) in equation (3), we get
y1+y2=23⇒Im(z1+z2)=23