[m]x+y=t; t → 0[/m]
[m]x^2-y^2=(x-y)(x+y)[/m]
[m]lim_{x →1; y →-1} \frac{tg(x+y)\cdot e^{x-y}}{x^2-y^2}=lim_{x →1; y →-1} \frac{tg(x+y)\cdot e^{x-y}}{(x-y)(x+y)}=lim_{x →1; y →-1} \frac{tg(x+y)}{x+y}\cdot\frac{ e^{x-y}}{x-y}=[/m]
[m]=lim_{x →1; y →-1} \frac{tg(x+y)}{x+y}\cdot lim_{x →1; y →-1} \frac{ e^{x-y}}{x-y}=1\cdot lim_{x →1; y →-1} \frac{ e^{x-y}}{x-y}=\frac{e^2}{2} [/m]