google.com different IP in different countries. How?

Solution 1:

A DNS name may have multiple A records, clients may then choose any record and use that address.

That's not the entire truth though, Google's DNS servers are also giving you different A records depending on your IP address so that you may use a server close to you.

Solution 2:

I believe it's called CDN

Solution 3:

I think it is using Anycast IP addressing for the DNS servers. So depending on which part of the world you are, a different DNS server (although with the same IP address) will answer your query. And that server will know which IP address is the best for your location.