contrapositive form

例句：

1. 1. In mathematics, the contrapositive form of a statement is often used to find its negation.
   在数学中，一个陈述的反证形式常被用来找到它的否定。
2. 2. The teacher explained the concept in a way that made it easy for students to understand.
   老师用一种方式解释这个概念，使学生很容易理解。
3. 3. The problem was solved by finding the contrapositive form of the equation.
   通过找到方程的反证形式解决了这个问题。