"My major is mathematics" 是表达专业为数学的常用说法。
major 是英语中的名词，意思是“主修，专业”。这个词来源于拉丁语的 "maior"，意思是 "大的，重要的"。
下面是一些例句：
I'm studying math as my major in college. (我在大学里主修数学。)
He changed his major from Engpsh to mathematics. (他把专业从英语改为数学。)
She decided to double major in math and computer science. (她决定辅修数学和计算机科学。)