Let z=x+iy, where x,y∈R.
Given ∣z∣=2, so
∣z∣2=x2+y2=2.
Also, ∣z2−i∣=1.
Compute z2:
z2=(x+iy)2=x2−y2+2ixy.
So,
z2−i=(x2−y2)+2ixy−i=(x2−y2)+i(2xy−1).
Therefore,
∣z2−i∣2=(x2−y2)2+(2xy−1)2=1.
Now, we have the system:
x2+y2(x2−y2)2+(2xy−1)2=2=1
Let us use polar form: z=reiθ, r=2, so z=2eiθ.
Then z2=2ei2θ, so
z2−i=2ei2θ−i.
Write 2ei2θ=2(cos2θ+isin2θ), so
z2−i=2cos2θ+i(2sin2θ−1).
Therefore,
∣z2−i∣2=(2cos2θ)2+(2sin2θ−1)2=1.
Expand:
4cos22θ+(4sin22θ−4sin2θ+1)4cos22θ+4sin22θ−4sin2θ+14(cos22θ+sin22θ)−4sin2θ+14(1)−4sin2θ+14−4sin2θ+1=14−4sin2θ=01−sin2θ=0sin2θ=1=1=1=1=1
So 2θ=2π+2πk, k∈Z.
Thus θ=4π+πk.
Therefore, the solutions are
z=2ei(4π+πk)
for k∈Z.
Explicitly, for k=0:
z1=2ei4π=2(cos4π+isin4π)=2(22+i22)=1+i.
For k=1:
z2=2ei(45π)=2(cos45π+isin45π)=2(−22−i22)=−1−i.
Thus, the solutions are z=1+i and z=−1−i.