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1 | - | Alternatively, just the truth table method. Since each proposition must be equal to its matching variable, we can mark rows as contradictions if the two sets of columns are unequal. All rows without contradictions are valid answers to the question. I don't have to convince you of any given value of any given variable, because this is exhaustively examining every possible combination. |
1 | + | Let A, B, C, D, and E be five boolean variables. |
2 | ||
3 | Let P1, P2, P3, P4, and P5 be the five propositions listed in the question. | |
4 | ||
5 | To find all possible answers, we can construct a truth table. Since each proposition must be equal to its matching variable, we can mark rows as contradictions if the two sets of columns are unequal. All rows without contradictions are valid answers to the question. I don't have to convince you of any given value of any given variable, because this is exhaustively examining every possible combination. | |
6 | ||
7 | A B C D E | P1 P2 P3 P4 P5 | Contradiction? | |
8 | ----------+----------------+--------------- | |
9 | F F F F F | T T F T F | Yes | |
10 | F F F F T | F T F T F | Yes | |
11 | F F F T F | F F F T F | No | |
12 | F F F T T | F F F T F | Yes | |
13 | F F T F F | F F F F F | Yes | |
14 | F F T F T | F F F F F | Yes | |
15 | F F T T F | F F F F F | Yes | |
16 | F F T T T | F F F F F | Yes | |
17 | F T F F F | F T F F F | No | |
18 | F T F F T | F T F F F | Yes | |
19 | F T F T F | F F F F F | Yes | |
20 | F T F T T | F F F F F | Yes | |
21 | F T T F F | F F T F F | Yes | |
22 | F T T F T | F F T F F | Yes | |
23 | F T T T F | F F T F F | Yes | |
24 | F T T T T | F F T F F | Yes | |
25 | T F F F F | T T F F F | Yes | |
26 | T F F F T | F T F F F | Yes | |
27 | T F F T F | F F F F F | Yes | |
28 | T F F T T | F F F F F | Yes | |
29 | T F T F F | F F F F F | Yes | |
30 | T F T F T | F F F F F | Yes | |
31 | T F T T F | F F F F F | Yes | |
32 | T F T T T | F F F F F | Yes | |
33 | T T F F F | F T F F F | Yes | |
34 | T T F F T | F T F F F | Yes | |
35 | T T F T F | F F F F F | Yes | |
36 | - | T T T T T | F F T F T | Yes |
36 | + | |
37 | T T T F F | F F T F F | Yes | |
38 | T T T F T | F F T F F | Yes | |
39 | T T T T F | F F T F F | Yes | |
40 | T T T T T | F F T F T | Yes | |
41 | ||
42 | In conclusion, there are two possible answers: | |
43 | ||
44 | (1) Only B is true. | |
45 | (2) Only D is true. | |
46 | ||
47 | They cannot be true at the same time. |