In logic, proof by contradiction is a form of proof that establishes the truth or validity of a proposition by showing that the proposition’s being false would imply a contradiction. Since by the law of bivalence a proposition must be either true or false, and its falsity has been shown impossible, the proposition must be true.
Proof by contradiction is also known as indirect proof, apagogical argument, reductio ad impossibile. It is a particular kind of the more general form of argument known as reductio ad absurdum. Read more on – Wikipedia
Video on Indirect Proof
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