[问答题]
$\text { On the Argand diagram below, the point } \mathrm{A} \text { represents the complex number } 4 \mathrm{i} \text { and the point } \mathrm{B} \text { represents the complex number }-5+\mathrm{i} \text {. The shape } \mathrm{ABCD} \text { is a square. }$
Determine the complex number represented by:
1. the point C ;
2. the point D .
