shù / xué / lǎo / shī / zài / hēi / bǎn / shàng / xiě / xià / jiǎo / fēn / fú / hào / bìng / jiě / shì / tā / de / yòng / fǎ

数学老师在黑板上写下角分符号，并解释它的用法。

The math teacher wrote the prime symbol on the board and explained how it is used.