Probar $$I=\int_0^\infty {\frac{x}{{\left( {x + 1} \right)\sqrt {4{x^4} + 8{x^3} + 12{x^2} + 8x + 1} }}dx} = \frac{{\ln 3}}{2} - \frac{{\ln 2}}{3}.$$
Primera nota de que $$4{x^4} + 8{x^3} + 12{x^2} + 8x + 1 = 4{\left( {{x^2} + x + 1} \right)^2} - 3,$$ nos vamos a $${x^2} + x + 1 = \frac{{\sqrt 3 }}{{2\cos \theta }} \Rightarrow x = \sqrt { - \frac{3}{4} + \frac{{\sqrt 3 }}{{2\cos \theta }}} - \frac{1}{2},$$ entonces $$I=\frac{1}{2}\int_{\frac{\pi }{6}}^{\frac{\pi }{2}} {\frac{{\left( {\sqrt {2\sqrt 3 \sec \theta - 3} - 1} \right)\sec \theta }}{{\left( {\sqrt {2\sqrt 3 \sec \theta - 3} + 1} \right)\sqrt {2\sqrt 3 \sec \theta - 3} }}d\theta } .$$ tenemos \begin{align*} &\frac{{\left( {\sqrt {2\sqrt 3 \sec \theta - 3} - 1} \right)\sec \theta }}{{\left( {\sqrt {2\sqrt 3 \sec \theta - 3} + 1} \right)\sqrt {2\sqrt 3 \sec \theta - 3} }} = \frac{{{{\left( {\sqrt {2\sqrt 3 \sec \theta - 3} - 1} \right)}^2}\sec \theta }}{{\left( {2\sqrt 3 \sec \theta - 4} \right)\sqrt {2\sqrt 3 \sec \theta - 3} }}\\ =& \frac{{\left( {2\sqrt 3 \sec \theta - 2 - 2\sqrt {2\sqrt 3 \sec \theta - 3} } \right)\sec \theta }}{{\left( {2\sqrt 3 \sec \theta - 4} \right)\sqrt {2\sqrt 3 \sec \theta - 3} }} = \frac{{\left( {\sqrt 3 \sec \theta - 1 - \sqrt {2\sqrt 3 \sec \theta - 3} } \right)\sec \theta }}{{\left( {\sqrt 3 \sec \theta - 2} \right)\sqrt {2\sqrt 3 \sec \theta - 3} }}\\ = &\frac{{\left( {\sqrt 3 \sec \theta - 1} \right)\sec \theta }}{{\left( {\sqrt 3 \sec \theta - 2} \right)\sqrt {2\sqrt 3 \sec \theta - 3} }} - \frac{{\sec \theta }}{{\sqrt 3 \sec \theta - 2}}. \end{align*} y $$\int {\frac{{\sec \theta }}{{\sqrt 3 \sec \theta - 2}}d\theta } = \ln \frac{{\left( {2 + \sqrt 3 } \right)\tan \frac{\theta }{2} - 1}}{{\left( {2 + \sqrt 3 } \right)\tan \frac{\theta }{2} + 1}}+ C.$$ mientras \begin{align*}&\int {\frac{{\left( {\sqrt 3 \sec \theta - 1} \right)\sec \theta }}{{\left( {\sqrt 3 \sec \theta - 2} \right)\sqrt {2\sqrt 3 \sec \theta - 3} }}d\theta } = \int {\frac{{\sqrt 3 - \cos \theta }}{{\left( {\sqrt 3 - 2\cos \theta } \right)\sqrt {2\sqrt 3 \cos \theta - 3{{\left( {\cos \theta } \right)}^2}} }}d\theta } \\ = &\frac{1}{2}\int {\frac{1}{{\sqrt {2\sqrt 3 \cos \theta - 3{{\left( {\cos \theta } \right)}^2}} }}d\theta } + \frac{{\sqrt 3 }}{2}\int {\frac{1}{{\left( {\sqrt 3 - 2\cos \theta } \right)\sqrt {2\sqrt 3 \cos \theta - 3{{\left( {\cos \theta } \right)}^2}} }}d\theta } . \end{align*} Pero, ¿cómo podemos continuar? Está relacionada con la integral elíptica.
