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That CAN'T be true! / 5th root if integer number by hand?
« on: 14/09/2010 12:19:10 »
Hi,
I can vaguely remember that someone amazed me once that he could calculate the 5th root of a natural number that I had to write down for him. I just had to promise that the result is a regular integer as well, then he would stare at the number for a couple of seconds and then he told me the result. It was not a math genius or so, a normal student. I think the numbers I presented him were like 1027^5 and such.
What is the trick? I know of many tricks, how to check for dividability-by-three ans so on, but the 5th root?
thanks!
towi.
I can vaguely remember that someone amazed me once that he could calculate the 5th root of a natural number that I had to write down for him. I just had to promise that the result is a regular integer as well, then he would stare at the number for a couple of seconds and then he told me the result. It was not a math genius or so, a normal student. I think the numbers I presented him were like 1027^5 and such.
What is the trick? I know of many tricks, how to check for dividability-by-three ans so on, but the 5th root?
thanks!
towi.