Evaluate the following integral ∫_0^∞(x tan^(-1)x)/(1+x^2 )^2 dx
∫_0^∞(x tan^(-1)x)/(1+x^2 )^2 dxLet x=tanθ→dx=〖sec〗^2θ dθ,x=0→θ=0,x=∞→θ=π/2∴I=∫_0^(π/2)(θ tanθ)/(1+〖tan〗^2 θ)^2 .〖sec〗^2 θdθ=∫_0^(π/2)〖θ tanθ 〗.〖cos〗^2 θdθ=∫_0^(π/2)〖θ sinθ 〗.cosθ dθ=1/2 ∫_0^(π/2)〖θ sin2θ 〗 dθBy parts:u=θ dv=sin2θ dθdu=dθ v=-1/2 cos2θ∴I=1/2 [├ -1/2 θ cosθ ┤|_0^(π/2)+├ 1/4 sin2θ ┤|_0^(π/2) ]=1/4 [π/2]=π/8
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∫_0^∞(x tan^(-1)x)/(1+x^2 )^2 dx
need an explanation for this answer? contact us directly to get an explanation for this answerLet x=tanθ→dx=〖sec〗^2θ dθ,x=0→θ=0,x=∞→θ=π/2
∴I=∫_0^(π/2)(θ tanθ)/(1+〖tan〗^2 θ)^2 .〖sec〗^2 θdθ=∫_0^(π/2)〖θ tanθ 〗.〖cos〗^2 θdθ
=∫_0^(π/2)〖θ sinθ 〗.cosθ dθ=1/2 ∫_0^(π/2)〖θ sin2θ 〗 dθ
By parts:
u=θ dv=sin2θ dθ
du=dθ v=-1/2 cos2θ
∴I=1/2 [├ -1/2 θ cosθ ┤|_0^(π/2)+├ 1/4 sin2θ ┤|_0^(π/2) ]=1/4 [π/2]=π/8