# If a and B Are Sets, Then Prove that a − B , a ∩ B and B − a Are Pair Wise Disjoint. - Mathematics

If A and B are sets, then prove that  $A - B, A \cap B \text{ and } B - A$ are pair wise disjoint.

#### Solution

$\left( i \right) \left( A - B \right) \text{ 0and } \left( A \cap B \right)$
$\text{ Let } a \in A - B$
$\Rightarrow a \in A \text{ and } a \not\in B$
$\Rightarrow a \not\in A \cap B$
$\text{ Hence }, \left( A - B \right) \text{ and } A \cap B \text{ are disjoint sets } .$
$\left( ii \right) \left( B - A \right) and \left( A \cap B \right)$
$\text{ Let } a \in B - A$
$\Rightarrow a \in B \text{ and } a \not\in A$
$\Rightarrow a \not\in A \cap B$
$\text{ Hence }, \left( B - A \right) \text{ and } A \cap B \text{ are disjoint sets } .$
$\left( iii \right) \left( A - B \right) \text{ and } \left( B - A \right)$
$\left( A - B \right) = \left\{ x: x \in A \text{ and }x \not\in B \right\}$
$\left( B - A \right) = \left\{ x: x \in B \text{ and } x \not\in A \right\}$
$Hence, \left( A - B \right) \text{ and } \left( B - A \right) \text{ are disjoint sets } .$

Concept: Universal Set
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#### APPEARS IN

RD Sharma Class 11 Mathematics Textbook
Chapter 1 Sets
Exercise 1.6 | Q 10 | Page 27