be good at的用法详解：
be good at表示“擅长”
1.be good at sth. 擅长某事
He is good at maths.
他擅长数学。
They are good at physics.
他们擅长物理。

2.be good at doing sth. 擅长做某事
Tom is good at playing football.
汤姆擅长踢足球。
John is good at singing.
约翰擅长唱歌。


3.be good at = do well in
He is good at maths.
=He does well in maths.

4.be good at的反义词
表示“不擅长....”或“在某方面做得不好”
be bad/poor at...;  
do badly in...;  
be weak in...；
He is bad at drawing.
他不擅长画画。
He is weak in English.
他不擅长英语。

以上就是be good at的用法。