A(z1) and B(z2) are the points on the circles |z| = 1 and |z| = 3 respectively, then:
||z1|−|z2||≤|z1−z2|≤|z1|+|z2|
If |z−z1|+|z+z2| = λ,λ∈R+,z1,z2 are fixed complex numbers, represents an ellipse, then: