Abstract
- When Direct Proof is hard to derive, we can try indirect proof
Disproof by Counterexample (反例法)
- An example that shows that a Mathematical Statement isn’t always true
Important
Useful for disproving Universal Statement
Example
Proof by Contradiction (矛盾证明法)
- An Indirect Proof, to prove a mathematical statement is false, prove its negation is true, and vice versa. This is useful when direct proof is difficult, and the negated statement has a form that is easier to prove.
Example
Proof by Contraposition (逆否命证明法)
- Use when the Contrapositive (逆否命题) is easier to proof