Multiply each of the following expressions.

1. $(x - i)(x - i)$ 

   Hint (a):

   $(i)^2 = -1$

2. $(x - 2i)(x - 2i)$ 

   Answer (b):

   $x^2 - 4xi - 4$ 

3. Write the expression $x^2 - 6ix - 9$ as a product.

   Answer (c):

   $(x - 3i)(x - 3i)$