Lǎoshī zài hēibǎn shàng tuīdǎo le zhèngxián dìnglǐ.
The teacher derived the law of sines on the blackboard.
Tips
memory
正弦 (zhèngxián) = sine, 定理 (dìnglǐ) = theorem. The full law: a/sinA = b/sinB = c/sinC = 2R, where R is the circumscribed circle's radius. Once you know 正弦 and 定理 separately, the term decodes itself.
