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You don't. Quit the reductio ad absurdum and do both.
It is a phrase, not a term. The phrase is reductio ad absurdum.
Proof by contradiction is also known by its Latin equivalent, reductio ad absurdum.
Mom: "Why did you drink alcohol when you know you're not of age?"
Son: "All of my friends were doing it."
Mom: "So, if all of your friends jumped off a bridge, you would too?"