zài / shù / xué / kè / shàng / lǎo / shī / yòng / yǎn / yì / fǎ / zhèng / míng / le / zhè / ge / dìng / lǐ

在数学课上，老师用演绎法证明了这个定理。

In math class, the teacher used deductive reasoning to prove this theorem.