Question
Consider : Statement − I : is a fallacy. Statement − II : is a tautology.
Options
Solution
Key Concepts and Formulas
- Logical Connectives: Understanding the truth tables for AND (), OR (), NOT (), implication (), and bi-conditional ().
- Tautology: A statement that is always true, regardless of the truth values of its components.
- Fallacy (Contradiction): A statement that is always false, regardless of the truth values of its components.
- Implication: is equivalent to .
- Bi-conditional: is equivalent to .
Step-by-Step Solution
Statement I Analysis:
Step 1: Create a truth table for the expression .
We need to consider all possible combinations of truth values for and .
Step 2: Determine the truth values of and .
If is true, then is false, and vice-versa. Similarly, if is true, then is false, and vice-versa.
Step 3: Determine the truth values of .
is true only when both and are true.
Step 4: Determine the truth values of .
is true only when both and are true.
Step 5: Determine the truth values of .
is true only when both and are true.
The truth table is as follows:
| T | T | F | F | F | F | F |
| T | F | F | T | T | F | F |
| F | T | T | F | F | T | F |
| F | F | T | T | F | F | F |
Step 6: Analyze the final column.
Since the last column is always false, the expression is a fallacy. Therefore, Statement I is true.
Statement II Analysis:
Step 1: Create a truth table for the expression .
Step 2: Determine the truth values of and .
Step 3: Determine the truth values of .
is false only when is true and is false. Otherwise, it is true. Equivalently, .
Step 4: Determine the truth values of .
is false only when is true and is false (i.e., is false and is true). Otherwise, it is true. Equivalently, .
Step 5: Determine the truth values of .
is true when both and have the same truth value. It is false when they have different truth values.
The truth table is as follows:
| T | T | F | F | T | T | T |
| T | F | F | T | F | F | T |
| F | T | T | F | T | T | T |
| F | F | T | T | T | T | T |
Step 6: Analyze the final column.
Since the last column is always true, the expression is a tautology. Therefore, Statement II is true.
Step 7: Determine if Statement II is a correct explanation for Statement I.
Statement II is about the equivalence of an implication and its contrapositive. Statement I is about a compound statement that is always false. There is no direct relationship between the two. Therefore, Statement II is not a correct explanation for Statement I.
Common Mistakes & Tips
- Be careful with the order of operations when evaluating logical expressions. Parentheses are important.
- Remember the truth tables for all the logical connectives.
- When proving a statement is a tautology or fallacy, it is usually sufficient to create a truth table.
- is only false when is true and is false.
Summary
Statement I is a fallacy, and Statement II is a tautology. Statement II does not explain Statement I. Therefore, Statement I is True; Statement II is True; Statement II is not a correct explanation for Statement I.
Final Answer
The final answer is \boxed{A}, which corresponds to option (A).