2 sentences

1. 几何学研究平面和立体的性质。

   jǐ​hé​xué yán​jiū píng​miàn hé lì​tǐ de xìng​zhì.

   Geometry studies the properties of planes and solids.

   Source: Dong Chinese Dictionary

2. 勾股定理是几何学中一个非常著名的定理。

   gōu gǔ dìng​lǐ shì jǐ​hé​xué zhōng yī gè fēi​cháng zhù​míng de dìng​lǐ.

   The Pythagorean theorem is a very famous theorem in geometry.

   Source: Dong Chinese Dictionary