Question Number 76052 by Ajao yinka last updated on 23/Dec/19
Commented by MJS last updated on 23/Dec/19
$${t}=\mathrm{e}^{−{x}} \:\rightarrow\:{dx}=−\mathrm{e}^{{x}} {dt} \\ $$$$\underset{\mathrm{0}} {\overset{\mathrm{1}} {\int}}{t}^{−{t}} {dt}\approx\mathrm{1}.\mathrm{291286} \\ $$