DirectedInfinity when solving limit

*To*: mathgroup at smc.vnet.net*Subject*: [mg127005] DirectedInfinity when solving limit*From*: Kiran Karra <kiran.karra at gmail.com>*Date*: Sat, 23 Jun 2012 04:15:45 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

Hi all, I am solving a complex algebraic equation for the variable n. I solve for it, and get a analytical answer. I then take the limit of that answer as a variable tends to +infinity. When I solve this in mathematica, I get the following solution: DirectedInfinity[ -B*ex-tx + sqrt( (B*ex+tx)^2 ) ] / L , where L is a constant. Conventional mathematical wisdom tells me that the numerator cancels out and becomes 0. I'm confused. Any thoughts as to how this limit can be either +infinity or -infinity I guess this is more of a mathematical question rather than Mathematica.. but if anybody can help me out that would be greatly appreciated. thanks!