Fuente TeX:

\lim \dfrac{1 - \sqrt{1+\rho^2}}{\rho^2} = \lim \dfrac{(1 - \sqrt{1+\rho^2})(1 + \sqrt{1+\rho^2})}{\rho^2(1 + \sqrt{1+\rho^2})} = \lim \dfrac{-\rho^2}{\rho^2(1 + \sqrt{1+\rho^2})} = \lim -\frac{1}{(1+\sqrt{1+\rho^2})} = -\frac{1}{2}