KTU Math
Part AModule All3 Marks

Question 1

Question

Let A, B, and C be sets. Show that A∪(B∩C)‾=(C‾∪B‾)∩A‾\overline{A \cup (B \cap C)} = (\overline{C} \cup \overline{B}) \cap \overline{A}.

Step-by-Step Solution

Step 1: Start with the Left Hand Side (LHS). LHS=A∪(B∩C)‾\text{LHS} = \overline{A \cup (B \cap C)}

Step 2: Apply De Morgan's Law: X∪Y‾=X‾∩Y‾\overline{X \cup Y} = \overline{X} \cap \overline{Y}. Let X=AX = A and Y=(B∩C)Y = (B \cap C). LHS=A‾∩(B∩C)‾\text{LHS} = \overline{A} \cap \overline{(B \cap C)}

Step 3: Apply De Morgan's Law again on the second term: X∩Y‾=X‾∪Y‾\overline{X \cap Y} = \overline{X} \cup \overline{Y}. (B∩C)‾=B‾∪C‾\overline{(B \cap C)} = \overline{B} \cup \overline{C} Substitute this back into the LHS equation: LHS=A‾∩(B‾∪C‾)\text{LHS} = \overline{A} \cap (\overline{B} \cup \overline{C})

Step 4: Use the Commutative Law of Union: X∪Y=Y∪XX \cup Y = Y \cup X. B‾∪C‾=C‾∪B‾\overline{B} \cup \overline{C} = \overline{C} \cup \overline{B} LHS=A‾∩(C‾∪B‾)\text{LHS} = \overline{A} \cap (\overline{C} \cup \overline{B})

Step 5: Use the Commutative Law of Intersection: X∩Y=Y∩XX \cap Y = Y \cap X. LHS=(C‾∪B‾)∩A‾\text{LHS} = (\overline{C} \cup \overline{B}) \cap \overline{A}

Conclusion: LHS=RHS\text{LHS} = \text{RHS} Hence, proved.