Easy Integrals 1

Calculus Level 4

2 2 x 2 + 4 x 4 + 16 d x \large \int_{\sqrt{2}}^{2} \dfrac{x^2+4}{x^4+16} \, dx

The integral above has a closed form. Find this closed form.

Give your answer to 3 decimal places.


The answer is 0.16392.

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1 solution

Hassan Abdulla
May 11, 2018

let I = 2 2 x 2 + 4 x 4 + 16 d x put x = 2 u I = 1 2 1 4 u 2 + 4 16 u 4 + 16 2 d u = 1 2 1 2 1 u 2 + 1 u 4 + 1 d u I = 1 2 1 2 1 u 2 + 1 ( u 2 2 x + 1 ) ( u 2 + 2 x + 1 ) d u I = 1 4 1 2 1 1 ( u 2 2 x + 1 ) + 1 ( u 2 + 2 x + 1 ) d u I = 1 4 1 2 1 1 ( u 2 2 x + 1 ) + 1 ( u 2 + 2 x + 1 ) d u I = 2 4 [ tan 1 ( 2 u + 1 ) + tan 1 ( 2 u 1 ) ] 1 1 2 0.1639241 \text{let } I=\int _{ \sqrt { 2 } }^{ 2 }{ \frac { { x }^{ 2 }+4 }{ { x }^{ 4 }+16 } dx } \\ \text{put } x=2u\Rightarrow I=\int _{ \frac { 1 }{ \sqrt { 2 } } }^{ 1 }{ \frac { { 4u }^{ 2 }+4 }{ 16{ u }^{ 4 }+16 } 2\cdot du } =\frac { 1 }{ 2 } \int _{ \frac { 1 }{ \sqrt { 2 } } }^{ 1 }{ \frac { { u }^{ 2 }+1 }{ { u }^{ 4 }+1 } du } \\ I=\frac { 1 }{ 2 } \int _{ \frac { 1 }{ \sqrt { 2 } } }^{ 1 }{ \frac { { u }^{ 2 }+1 }{ \left( { u }^{ 2 }-\sqrt { 2 } x+1 \right) \left( { u }^{ 2 }+\sqrt { 2 } x+1 \right) } du } \\ I=\frac { 1 }{ 4 } \int _{ \frac { 1 }{ \sqrt { 2 } } }^{ 1 }{ \frac { 1 }{ \left( { u }^{ 2 }-\sqrt { 2 } x+1 \right) } +\frac { 1 }{ \left( { u }^{ 2 }+\sqrt { 2 } x+1 \right) } du } \\ I=\frac { 1 }{ 4 } \int _{ \frac { 1 }{ \sqrt { 2 } } }^{ 1 }{ \frac { 1 }{ \left( { u }^{ 2 }-\sqrt { 2 } x+1 \right) } +\frac { 1 }{ \left( { u }^{ 2 }+\sqrt { 2 } x+1 \right) } du } \\ I=\frac { \sqrt { 2 } }{ 4 } \left[ \tan ^{ -1 }{ \left( \sqrt { 2 } u+1 \right) } +\tan ^{ -1 }{ \left( \sqrt { 2 } u-1 \right) } \right] \left| \begin{matrix} 1 \\ \\ \frac { 1 }{ \sqrt { 2 } } \end{matrix} \right. \approx 0.1639241

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