$\large \left| \frac { { Z }_{ 1 }-{ Z }_{ 2 } }{ { Z }_{ 1 }+{ Z }_{ 2 } } \right|$

If ${ Z }_{ 1 },{ Z }_{ 2 }$ are complex numbers such that $\frac { { 2Z }_{ 1 } }{ { 3Z }_{ 2 } }$ is purely imaginary then what is the value of above expression?

Your answer seems reasonable.
Find out if you're right!