Types of Mathematical Proofs to Know for Intro to Abstract Math

Understanding different types of mathematical proofs is essential in abstract math. Each proof method, from direct proof to proof by exhaustion, offers unique strategies for establishing the truth of statements, helping to build a solid foundation for mathematical reasoning.

1. Direct proof

   • Involves a straightforward application of definitions, axioms, and previously established theorems.
   • Starts with known facts and logically deduces the statement to be proven.
   • Commonly used for proving implications and equalities.

2. Proof by contradiction

   • Assumes the negation of the statement to be proven and derives a contradiction.
   • If a contradiction arises, the original statement must be true.
   • Useful for proving statements that are difficult to establish directly.

3. Proof by contraposition

   • Proves an implication by showing that if the conclusion is false, then the hypothesis must also be false.
   • The contrapositive of a statement is logically equivalent to the original statement.
   • Often simplifies the proof process for implications.

4. Proof by induction

   • Establishes the truth of a statement for all natural numbers by proving a base case and an inductive step.
   • The base case verifies the statement for the first natural number.
   • The inductive step shows that if the statement holds for an arbitrary natural number, it holds for the next one.

5. Proof by cases

   • Divides the proof into several distinct cases and proves the statement for each case.
   • Ensures that all possible scenarios are considered.
   • Useful when a statement can be true under different conditions.

6. Existence proof

   • Demonstrates that at least one example of a mathematical object satisfying certain conditions exists.
   • Does not necessarily provide a method to construct the object.
   • Often used in the context of proving the existence of solutions to equations or inequalities.

7. Uniqueness proof

   • Shows that a mathematical object satisfying certain conditions is unique.
   • Typically involves assuming there are two such objects and demonstrating they must be identical.
   • Important in contexts where a single solution is required.

8. Constructive proof

   • Provides a method to explicitly construct an example of the mathematical object being proven to exist.
   • Demonstrates not only existence but also how to find the object.
   • Often used in algorithms and computational contexts.

9. Proof by counterexample

   • Disproves a statement by providing a specific example that contradicts it.
   • Effective for showing that a general statement is false.
   • Highlights the importance of careful conditions in mathematical claims.

10. Proof by exhaustion

    • Involves checking all possible cases or scenarios to prove a statement.
    • Guarantees that the statement holds true by verifying each possibility.
    • Practical for statements with a limited number of cases to consider.