A calculus problem by Jonas Katona

Calculus Level 3

I = x 2 x 4 + 4 d x \large I=\int _{ -\infty }^{ \infty }{ \dfrac { { x }^{ 2 } }{ { x }^{ 4 }+4 } } \, dx If I I can be expressed in the form π a \dfrac { \pi }{ a } , find a a { a }^{ a } .


The answer is 4.

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1 solution

By computing definite integrals here: x 2 x 4 + 4 d x = 1 4 ( 1 2 ln ( x 1 ) 2 + 1 T A N 1 ( 1 x ) ) + 1 4 ( T A N 1 ( x + 1 ) 1 2 ln ( x + 1 ) 2 + 1 ) ) + C \int_{-\infty}^{\infty}\frac{x^2}{x^4+4}\,dx = \frac{1}{4}{\left(\frac{1}{2}\ln \mid (x-1)^2 +1 \mid - \ce{TAN}^{-1}(1-x))+\frac{1}{4}(\ce{TAN}^{-1}(x+1) -\frac{1}{2} \ln \mid (x+1)^2+1\mid)\right)}+\ce{C}


For computing boundaries see: a b f ( x ) d x = F ( b ) F ( a ) = lim x b ( F ( x ) ) lim x a + ( F ( x ) ) \begin{aligned} \int_{a}^{b} f(x) dx&= F(b) - F(a) \\&= \lim_{x\to b -}(F(x)) - \lim_{x \to a+}(F(x)) \end{aligned} .


Therefore the answer of this is π 2 \dfrac{\pi}{2} . Expressing in the from π a \dfrac{\pi}{a} then to find the value of a a a^a so let a = 2 a\ = 2 . The value of a a a^a is 4 4 a a \because a^a is 2 2 2^2\boxed{} .

Take note : you can convert the π 2 \frac{\pi}{2} into degrees so the equivalent is 9 0 90^\circ .

F I N ! ! ! ! \LARGE \ce{FIN!!!!}

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