"决定考研"可以用英文表达为 "decide to take the postgraduate entrance examination" 或 "decide to apply for postgraduate studies".

这个短语的来源是由两个单词组成的："决定"和"考研".

"决定"在英语中可以用 "decide" 表示，意思是"下定决心，做出决定"。例如：

I have decided to go to college. (我已经决定要去上大学了。)

"考研"在英语中可以用 "take the postgraduate entrance examination" 或 "apply for postgraduate studies" 表示。"postgraduate entrance examination" 是指研究生入学考试，"apply for postgraduate studies" 是指申请研究生学习。例如：

He decided to take the postgraduate entrance examination. (他决定参加研究生入学考试。)
She decided to apply for postgraduate studies. (她决定申请研究生学习。)