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Question Number 121862 by Bird last updated on 12/Nov/20

1)explicite f(a)=∫_0 ^∞ ((t^(a−1) lnt)/(1+t))dt  with 0<a<1  2)calculate ∫_0 ^∞   ((lnt)/((1+t)(√t)))dt

1)explicitef(a)=0ta1lnt1+tdt with0<a<1 2)calculate0lnt(1+t)tdt

Answered by mnjuly1970 last updated on 12/Nov/20

solution:1 :: g(b)=∫_0 ^( ∞) (t^(a+b−1) /(1+t))dt            f(a)=g′(0)            g(b)=Γ(a+b)Γ(1−a−b)=(π/(sin(π(a+b))))              g′(b)=((−π^2 cos(π(a+b)))/(sin^2 (π(a+b))))                g′(0)=((−π^2 cos(πa))/(sin^2 (πa)))=f(a)^         f(a)=−π^2 cot(πa)csc(πa) ...       2::   f((1/2))=0             we know that ::              ∫_0 ^( ∞) ((ln(x))/(1+x^2 ))dx=^(easy) 0

solution:1::g(b)=0ta+b11+tdt f(a)=g(0) g(b)=Γ(a+b)Γ(1ab)=πsin(π(a+b)) g(b)=π2cos(π(a+b))sin2(π(a+b)) Missing \left or extra \right f(a)=π2cot(πa)csc(πa)... 2::f(12)=0 weknowthat:: 0ln(x)1+x2dx=easy0

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