This is the Proof that A squared plus B squared equals C squared works.
Now the way A sqrd. + B sqrd.= C sqrd. is you take the difference in the X values, so in this scenario 4 and 1, and then square them, next the difference in the Y values, so 3 and 1, and square that. At this point you should be at 3 squared and 2 squared which is 9+4 which would then equal 13, and then you find the square root of 13 which gives you a distance of 3.06.