I know you are student good at maths I know you are student

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.
再问： 啊 谢谢 能在详细讲讲第一个句子吗
再答： ok. believe / think / know / suppose / find / consider sb to do / have done sth 1 we know him to be honest in the job 2 we find him to have been honest in the job he did. 3 he is cosidered to have invented the first ever PC. 4 He is supposed to be writing his 67th book for children.