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Integration Techniques

Writing an integral down is only the first step. A toolkit of techniques can help find its value, from substitutions to trigonometry to partial fractions to differentiation.

Level 4


\[ \large \int_{0}^{\infty} \dfrac{\tan^{-1}(\pi x) - \tan^{-1}(x)}{x}\, dx = A\pi^{B}\dfrac{\ln \pi}{C} \]

The equation holds true for positive integers \(A,B,C\) with \(A,C\) coprime. Find \(A\times B\times C\).

\[\large I = \int_{0}^{\infty}\dfrac{x \ln{(4x)}}{\frac{1}{4}x^{4}+x^{2}+1} \,dx\]

\(I\) is the value of the closed form of the above integral. What is the value of \(\lfloor 100I \rfloor\)?

You may use the fact that \(\ln(2) \approx 0.693147\).

\[\large \displaystyle \int_0^\pi \dfrac{x\sin 2x \sin\left(\frac \pi 2 \cos x\right)}{2x-\pi} \, dx\]

The above integral can be expressed as \(\dfrac{A}{B\pi^C}\) where \(A\), \(B\) and \(C\) are positive integers with \(A\), \(B\) coprime. Find \(A+B+C\)

\[\large \int_{\frac{1}{8}}^{\frac{1}{2}} \left \lfloor \ln \left \lceil \dfrac{1}{x} \right \rceil \right \rfloor dx = \, ?\]

\[\] Notations: \( \lfloor \cdot \rfloor \) denotes the floor function and \( \lceil \cdot \rceil \) denotes the ceiling function.

\[\large \int_0^\infty \frac {\sin x}{xe^x} \, dx = \, ? \]


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