He is a genius in mathematics.

他是个数学天才。

He is a genius at computers.

他是一位计算机天才。

Do you doubt that he is a genius?

你怀疑他是个天才吗？

He is a genius in his way.

在某种程度上，他是个天才。

For me, he is a genius.

对我来说，他是个天才。