Official solution
\[\because\] \[{{{z_1}} \over {{z_2}}} = - i \Rightarrow {z_1} = - i{z_2}\]
\[ \Rightarrow \arg ({z_1}) = - {\pi \over 2} + \arg ({z_2})\] ..... (i)
Also \[\arg ({z_1}) - \arg ({\overline z _2}) = \pi \]
\[ \Rightarrow \arg ({z_1}) + \arg ({z_2}) = \pi \] ..... (ii)
From (i) and (ii), we get
\[\arg ({z_1}) = {\pi \over 4}\] and \[\arg ({z_2}) = {{3\pi } \over 4}\]