Let [tex]$A=\{x \mid x\ \textless \ 1\}$[/tex] and [tex]$B=\{x \mid x\ \textgreater \ 3\}$[/tex]. What is [tex][tex]$A \cap B$[/tex][/tex]?

A. [tex]$\varnothing$[/tex]
B. [tex]$\{x \mid x\ \textless \ 1 \text{ or } x\ \textgreater \ 3\}$[/tex]
C. [tex][tex]$\{2\}$[/tex][/tex]
D. [tex]$\{x \mid 1\ \textless \ x\ \textless \ 3\}$[/tex]



Answer :

Let's analyze the sets [tex]\( A \)[/tex] and [tex]\( B \)[/tex] and determine their intersection.

1. Define the Sets:
- Set [tex]\( A \)[/tex] contains all [tex]\( x \)[/tex] such that [tex]\( x < 1 \)[/tex].
- Set [tex]\( B \)[/tex] contains all [tex]\( x \)[/tex] such that [tex]\( x > 3 \)[/tex].

2. Describe the Elements in Each Set:
- For [tex]\( A \)[/tex], the elements are any numbers that are less than 1.
- For [tex]\( B \)[/tex], the elements are any numbers that are greater than 3.

3. Intersection of Sets [tex]\( A \)[/tex] and [tex]\( B \)[/tex]:
- The intersection [tex]\( A \cap B \)[/tex] consists of all elements that are in both sets [tex]\( A \)[/tex] and [tex]\( B \)[/tex].
- An element [tex]\( x \)[/tex] has to satisfy both conditions: [tex]\( x < 1 \)[/tex] and [tex]\( x > 3 \)[/tex].

4. Analyze the Conditions:
- A number [tex]\( x \)[/tex] cannot be simultaneously less than 1 and greater than 3.
- There are no numbers that can fulfill both conditions at the same time.

Therefore, there are no elements that belong to both sets [tex]\( A \)[/tex] and [tex]\( B \)[/tex], meaning the intersection [tex]\( A \cap B \)[/tex] is the empty set.

Hence, the answer is [tex]\(\varnothing\)[/tex].