How does lim as t-->-∞ (t/e^-t) becomes lim as t-->-∞ (1/(-1)e^-t). Where does does -1 comes from?

Answer 1

Recall the chain rule: if u is a function of t, then
the derivative of e^u = e^u du/dt
so, d/dt (e^-t) = -1 e^-t

Answer 2

Thank you