Which law is this expression X+ X’.Y=X+Y
One way of looking at this is as a consequence of distributivity, where $P+QR\equiv (P+Q)(P+R)$. Then you'll have
$$\begin{align}
X+(X'Y) &amp;\equiv (X+X')(X+Y)&amp;\text{distributivity}\\
&amp;\equiv T(X+Y)&amp;\text{inverse}\\
&amp;\equiv X+Y&amp;\text{domination} 
\end{align}$$