Absorption Law Proof by Algebra
First of all, this is a math question.

I think you are confused on how brackets are used. They indicate precedence of operations, and can be used anywhere, even in places where such indication is not necessary. For example,
$$3 \times 5 + 8$$
and
$$(3 \times 5) + 8$$
are both legitimate expressions and they mean exactly the same thing.

Your expression
$$(x \cdot 1) + (x \cdot y)$$
is exactly the same as
$$x \cdot 1 + x \cdot y.$$
So we may calculate
$$(x \cdot 1) + (x \cdot y) = 
  x \cdot (1 + y) =
  x \cdot 1 = x.$$