2 sentences

1. 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

2. 勾股定理中的“弦”指的就是直角三角形的斜边。

   gōu gǔ dìng​lǐ zhōng de“ xián” zhǐ de jiù shì zhí​jiǎo sān​jiǎo​xíng de xié biān.

   The 'xian' in the Pythagorean theorem refers to the hypotenuse of a right triangle.

   Source: Dong Chinese Dictionary