Rappel sur la loi exponentielle

> lambda:= 'lambda':

> lambda*exp(-lambda*t); a:= unapply(%,t);

Masse totale=1

> Int(a(t),t=0..infinity);
xplif(%,[lambda,positive]);

Espérance

> Int(t*a(t),t=0..infinity); xplif(%,[lambda,positive]);

Variance

> Int(t^2*a(t),t=0..infinity); xplif(%,[lambda,positive]);
%-1/lambda^2;