Junior high school teachers teach how to do proof questions, and they include proof by contradiction. The so-called proof by contradiction is to first put forward an assumption that is contrary to the conclusion in the theorem, and then draw results that contradict the known conditions from this assumption, thus denying the original assumption and affirming the theorem. Also called reductio ad absurdum.
In fact, proof by contradiction is to prove that the converse proposition of a proposition is correct. This is equivalent to direct proof, but it may be easier to prove its converse proposition. The above results in a contradiction, in fact, it leads to the conclusion that "the hypothesis and the proposition are not compatible", so we cannot accept this hypothesis, so the opposite of this hypothesis is correct, and the proposition is proved.