Image of Union under Relation

Let $$\mathcal{R} \subseteq S \times T$$ be a relation.

Theorem
The image of the union is equal to the union of the images.

Let $$S_1$$ and $$S_2$$ be subsets of $$S$$.

Then $$\mathcal{R} \left({S_1 \cup S_2}\right) = \mathcal{R} \left({S_1}\right) \cup \mathcal{R} \left({S_2}\right)$$.

Generalized Result
Let $$S_i \subseteq S: i \in \mathbb{N}_n$$.

Then $$\mathcal{R} \left({\bigcup_{i = 1}^n S_i}\right) = \bigcup_{i = 1}^n \mathcal{R} \left({S_i}\right)$$.