â«(0->1) e^x/(1+x) dx =A
let
1+x = -(u-a-1)
dx = -du
x=0, u=a
x=1, u=a-1
â«(0->1) e^x/(1+x) dx =A
â«(a->a-1) [ e^(-u+a)/-(u-a-1) ] -du =A
â«(a->a-1) [ e^(-u+a)/(u-a-1) ] du =A
-â«(a-1->a) [ e^(-u+a)/(u-a-1) ] du =A
-e^a . â«(a-1->a) [ e^(-u)/(u-a-1) ] du =A
â«(a-1->a) [ e^(-u)/(u-a-1) ] du =-A. e^a
â«(a-1->a) [ e^(-x)/(x-a-1) ] dx =-A. e^a
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