This is one of these silly ones that crop up every-so-often (and yes, beta, gamma are just the relativistic v/c and energy):
comes up with ±I*sqrt(-gamma^2+1)/gamma.
While this is not wrong it is nothing I want to throw at any student trying hard enough as it is to keep his/her head above water. What I want is beta=sqrt(1-1/gamma^2) and I am having a devil of a time getting Maple to do this. even doing it "by hand" the I comes in the moment I take the sqrt. "assuming" does not help (and when I try ...assuming beta::positive, gamma > 1 I get an error claiming these to be inconsistent).