Question: Construct a truth table for $ (q \to p) \lor \sim r $. Use T for true and F for false.
$p$ $q$ $r$ $(q \to p) \lor \sim r$
T T T
T T F
T F T
T F F
F T T
F T F
F F T
F F F
1. **State the problem:** Construct the truth table for the logical expression $$ (q \to p) \lor \sim r $$ where $p$, $q$, and $r$ are boolean variables.
2. **Recall definitions:**
- The implication $q \to p$ is false only when $q$ is true and $p$ is false; otherwise, it is true.
- The negation $\sim r$ is true when $r$ is false, and false when $r$ is true.
- The disjunction $\lor$ is true if at least one operand is true.
3. **List all possible truth values for $p$, $q$, and $r$: (8 rows)**
| $p$ | $q$ | $r$ |
|---|---|---|
| T | T | T |
| T | T | F |
| T | F | T |
| T | F | F |
| F | T | T |
| F | T | F |
| F | F | T |
| F | F | F |
4. **Calculate $q \to p$ for each row:**
- Row 1: $q=T$, $p=T$ so $q \to p = T$
- Row 2: $q=T$, $p=T$ so $q \to p = T$
- Row 3: $q=F$, $p=T$ so $q \to p = T$ (implication true if $q$ false)
- Row 4: $q=F$, $p=T$ so $q \to p = T$
- Row 5: $q=T$, $p=F$ so $q \to p = F$
- Row 6: $q=T$, $p=F$ so $q \to p = F$
- Row 7: $q=F$, $p=F$ so $q \to p = T$
- Row 8: $q=F$, $p=F$ so $q \to p = T$
5. **Calculate $\sim r$ for each row:**
- Row 1: $r=T$ so $\sim r = F$
- Row 2: $r=F$ so $\sim r = T$
- Row 3: $r=T$ so $\sim r = F$
- Row 4: $r=F$ so $\sim r = T$
- Row 5: $r=T$ so $\sim r = F$
- Row 6: $r=F$ so $\sim r = T$
- Row 7: $r=T$ so $\sim r = F$
- Row 8: $r=F$ so $\sim r = T$
6. **Calculate $(q \to p) \lor \sim r$ for each row:**
- Row 1: $T \lor F = T$
- Row 2: $T \lor T = T$
- Row 3: $T \lor F = T$
- Row 4: $T \lor T = T$
- Row 5: $F \lor F = F$
- Row 6: $F \lor T = T$
- Row 7: $T \lor F = T$
- Row 8: $T \lor T = T$
7. **Final truth table:**
| $p$ | $q$ | $r$ | $(q \to p) \lor \sim r$ |
|---|---|---|---|
| T | T | T | T |
| T | T | F | T |
| T | F | T | T |
| T | F | F | T |
| F | T | T | F |
| F | T | F | T |
| F | F | T | T |
| F | F | F | T |