( x^2 -1)/(x^2+1) = 1 - 2/(x^2+1)let1/y =2/(x^2+1)lim(x->+∞) [( x^2 -1)/(x^2+1) ]^(x^2)=lim(x->+∞) [ 1- 2/(x^2+1) ]^(x^2)=lim(y->+∞) [ 1- 1/y ]^(2y -1)=lim(y->+∞) [ 1- 1/y ]^(2y)=e^(-2)
