lǎo / shī / xiān / jiǎng / jiě / zhèng / xián / dìng / lǐ / de / gōng / shì / rán / hòu / dài / wǒ / men / zuò / le / liǎng / dào / liàn / xí / tí

老师先讲解正弦定理的公式，然后带我们做了两道练习题。

The teacher first explained the formula for the law of sines and then guided us through two practice problems.