The following table has two attributes $$A$$ and $$C$$ where $$A$$ is the primary key and $$C$$ is the foreign key referencing $$A$$ with on-delete cascade.

The set of all tuples that must be additionally deleted to preserve referential integrity. When the tuple $$(2,4)$$ is deleted is:

Let $${E_1}$$ and $${E_2}$$ be two entities in an E-R diagram with simple single-valued attributes, $${E_1}$$ and $${E_2}$$ are two relationships between $${E_1}$$ and $${E_2}$$, Where $${E_1}$$ is one-to-many and $${E_2}$$ is many-to-many. $${E_1}$$ and $${E_2}$$ do not have any attributes of their own. What is the minimum number of tables required represent this situation in the relation model?

The set $$\left\{ {1,\,\,2,\,\,4,\,\,7,\,\,8,\,\,11,\,\,13,\,\,14} \right\}$$ is a group under multiplication modulo $$15$$. The inverse of $$4$$ and $$7$$ are respectively:

Consider the following system of equations in three real variables $$x1, x2$$ and $$x3$$ :
$$2x1 - x2 + 3x3 = 1$$
$$3x1 + 2x2 + 5x3 = 2$$
$$ - x1 + 4x2 + x3 = 3$$
This system of equations has