#30

I want to ask C and D.

#56

how to show that $$\sqrt{d}$$ is also a metric?

#60

I can just work out II, and only get ...maybe...s(st-ts)t=0...

why I and III are all right?

#63

why these two curve intersect 2 points when x>0?why not 0 or 1?

Thank you very much!

If some Qs had been asked before, just reply me the link is okey~~~

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