Question

he is running fast, is he?​

Answer 1

Answer:

The above statement is incorrect.

Correct :

He is running fast, isn't he?

The question tag must be negative if the helping Verb is positive. If helping Verb is negative then the tag must be positive.

I am not perfect but just trying to answer your question :) :) :)

Answer 2

Answer:

if he is running fast his probably flash ⚡⚡