RRB Technician Grade 1 Model Paper 5

Concept:The complement of a set $A$, denoted $A'$, contains all elements not in $A$. Taking the complement twice returns the original set.Explanation:Let $A$ be any set within a universal set $U$.The complement $A'$ is defined as $A' = \{x \in U : x \notin A\}$.Now consider the complement of $A'$, written as $(A')'$.By definition, $(A')' = \{x \in U : x \notin A'\}$.Since $x \notin A'$ means $x$ is not outside $A$, it means $x$ belongs to $A$.Therefore, $(A')' = \{x \in U : x \in A\} = A$.This is known as the double complement law for sets.Answer:$(A')' = A$, so the correct option is A.