(b) माना $\frac{{2{z_1}}}{{3{z_2}}} = iy$ या $\frac{{{z_1}}}{{{z_2}}} = \frac{3}{2}iy$, तब

 $\left| {\frac{{{z_1} – {z_2}}}{{{z_1} + {z_2}}}} \right| = \left| {\frac{{\frac{{{z_1}}}{{{z_2}}} – 1}}{{\frac{{{z_1}}}{{{z_2}}} + 1}}} \right| = \left| {\frac{{\frac{3}{2}iy – 1}}{{\frac{3}{2}iy + 1}}} \right| = \left| {\frac{{1 – \frac{3}{2}iy}}{{1 + \frac{3}{2}iy}}} \right| = 1$$\left\{ {\because \,\,\,\,|z|\, = \,|\overline z |} \right\}$