I know you are student good at maths I know you are student who is good at maths 这两个句字

这两个句子中good at maths 是做定语还是宾补？请帮帮我

你好。请比较：
1 I (主语)know（谓语） you （宾语）to be good at maths (宾语补足语)
2 You are a student （ good at maths ）-----括号中的内容是定语後置，修饰前面的student.
3 I know you are a student (who are good at maths)-------括号中的内容是定语从句， 修饰前面的student。

应该是i know you are a student who is good at maths. 原句少了冠词a. 你是对的，who is good at maths 是定语从句，修饰前面的student，补足语通常不会是句子。