Fuente TeX:

x(t) = \frac{1+ce^{2t}}{1-ce^{2t}} = \frac{1-e^{2(t-k)}}{1+e^{2(t-k)}} = \frac{e^{k-t} - e^{-(k-t)}}{e^{k-t} + e^{-(k-t)}}