Diccrete Math problem: finding a proposition given a specific truth table

In summary, the conversation is about finding a proposition using only p, q, ¬ and the connective ∧ with a given truth table. The conversation discusses two possible solutions, one using OR and the other using AND. The final answer is not p, which can be derived from the first solution of (¬p ∧ q) ∨ (¬p ∧ ¬q) by simplifying using the distributive rule. The book suggests another answer, ¬(p ∧ ¬q) ∧ ¬(p ∧ q), which is also logically equivalent to not p. The speaker wonders how to convert one solution to the other.
  • #1
nicnicman
136
0
I've been working at this problem for a while and it seems that there should be an easier more systematic way of solving it. Here it is:

Find a proposition using only p, q, ¬ and the connective ∧ with the given truth table.

p q ?
T T F
T F F
F T T
F F T

I know of a systematic approach to creating propositions but includes the use of OR. Is there a systematic way of solving this only using ANDs?
 
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  • #2
Just read off the ones where the truth table evaluates to "T", namely:
F T T
F F T
This results in:
(not p and q) (from the F T T line)
(not p and not q) (from the F F T line)

join them with "or":
(not p and q) or (not p and not q)

simplify if possible, using the distributive rule in this case:
(not p) and (q or not q)
q or not q = T
(not p) and T = not p

final result:
not p
 
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Likes InfZero
  • #3
Thanks this is very helpful. It's actually the way I originally went about solving the problem but the book gives another answer:

¬(p ∧ ¬q) ∧ ¬(p ∧ q)

Probably both answers are acceptable, but I wonder how I could get the book's answer from your original answer, (¬p ∧ q) ∨ (¬p ∧ ¬q). There must be a way to convert it since they are logically equivalent.
 

1. What is discrete math?

Discrete math is a branch of mathematics that deals with discrete objects or countable quantities, such as integers, graphs, and mathematical structures. It is used to solve problems related to algorithms, logic, and combinatorics.

2. What is a truth table?

A truth table is a table that displays all possible combinations of inputs for a logical expression and the corresponding outputs. It is commonly used to evaluate the validity of logical arguments and to determine the truth values of complex propositions.

3. How do you find a proposition given a specific truth table?

To find a proposition given a specific truth table, you need to analyze the truth values in the table and determine the pattern or rule that governs the values. Once you have identified the pattern, you can construct a logical expression using variables and logical operators that produces the same truth values as the given table.

4. What are the steps to solve a discrete math problem?

The steps to solve a discrete math problem vary depending on the specific problem. However, some general steps include understanding the problem, identifying the relevant concepts and theories, developing a solution strategy, implementing the strategy, and checking the solution for accuracy.

5. Is discrete math important in real life?

Yes, discrete math is important in real life as it provides the foundation for many practical applications, such as computer science, cryptography, and data analysis. It also helps in developing critical thinking and problem-solving skills that are essential in various fields, including science, engineering, and business.

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