Honest Man and single Question

Problem

An honest man holds a card with one of the three possible numbers on it “1”, “2” or “3”. You can ask one question and the man allowed to answer only “Yes”,”No” and “I don’t know”. The honest man obviously never lies. Which question would you ask to say with 100% certainty which number is on the card the honest man holds?

Solution

         Question should be: "If I substract 2 from your number, and then take squery root, would the result be greater than zero?"

Man's number 3 -> Sqrt(3-2)=Sqrt(1)=1, (1>0)==TRUE, so the answer is "YES"
Man's number 2 -> Sqrt(2-2)=Sqrt(0)=0, (0>0)==FALSE, so the answer is "NO"
Man's number 1 -> Sqrt(1-2)=Sqrt(-1)=i, (i>0)==???, so the answer is "I DON't KNOW"