The first is proving commutivity of addition and multiplication of complex numbers, the second does the same for the complex conjugates, and the third is proving the associative law of multiplication.
In all of these cases let
and work out each side and compare them.
For example, let's prove :
(since da = ad, etc. We may assume that the addition and multiplication of real numbers is commutative.)
Thus where u and v are complex.
The other problems work the same way. I'd write out "tres" step by step since it's going to be a long one to work out.