lǎo / shī / zài / kè / táng / shàng / jiǎng / jiě / le / rú / hé / jiě / èr / yuán / yī / cì / fāng / chéng / zǔ老师在课堂上讲解了如何解二元一次方程组。The teacher explained in class how to solve a system of two linear equations.