4 sentences

1. 三的二次方等于九。

   sān de èr cì fāng děng​yú jiǔ.

   Three squared equals nine.

   Source: Dong Chinese Dictionary

2. 我们需要解这个二次方程式。

   wǒ​men xū​yào jiě zhè gè èr cì fāng​chéng​shì.

   We need to solve this quadratic equation.

   Source: Dong Chinese Dictionary

3. 一个二次方程的最高项次数是二。

   yī​gè èr​cì fāng​chéng de zuì gāo xiàng cì​shù shì èr.

   The highest degree of a quadratic equation is two.

   Source: Dong Chinese Dictionary

4. 老师在课堂上讲解了如何通过配方来解一元二次方程。

   lǎo​shī zài kè​táng shàng jiǎng​jiě le rú​hé tōng​guò pèi​fāng lái jiě yī​yuán'èr​cì fāng​chéng.

   The teacher explained in class how to solve quadratic equations by completing the square.

   Source: Dong Chinese Dictionary