分母分子にxのべき乗を含む積分
分母分子にxのべき乗を含む積分
次の積分が成り立つ。
\[ \begin{align*}\int_{0}^{\infty}\frac{x^{\alpha}}{x^{n}+1}dx & =\frac{\pi}{n}\sin^{-1}\left(\frac{\left(\alpha+1\right)\pi}{n}\right)\end{align*} \]
次の積分が成り立つ。
(1)
\[ \int\frac{x^{\alpha}}{x^{\beta}+\gamma}dx=\frac{x^{\alpha+1}}{\left(\alpha+1\right)\gamma}F\left(1,\frac{\alpha+1}{\beta};\frac{\alpha+1}{\beta}+1;-\frac{x^{\beta}}{\gamma}\right)+C \](2)
\(n\in\mathbb{N},\left|\Re\left(\alpha\right)\right|<1\)とする。\[ \begin{align*}\int_{0}^{\infty}\frac{x^{\alpha}}{x^{n}+1}dx & =\frac{\pi}{n}\sin^{-1}\left(\frac{\left(\alpha+1\right)\pi}{n}\right)\end{align*} \]
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\(F\left(a,b;c,x\right)\)は超幾何関数(1)
\begin{align*} \int\frac{x^{\alpha}}{x^{\beta}+\gamma}dx & =\frac{1}{\gamma}\int\frac{x^{\alpha}}{1+\frac{x^{\beta}}{\gamma}}dx\\ & =\frac{1}{\gamma}\int x^{\alpha}F\left(1;;-\frac{x^{\beta}}{\gamma}\right)dx\\ & =\frac{x^{\alpha+1}}{\left(\alpha+1\right)\gamma}F\left(1,\frac{\alpha+1}{\beta};\frac{\alpha+1}{\beta}+1;-\frac{x^{\beta}}{\gamma}\right)+C \end{align*}(2)
\[ \begin{align*}\int_{0}^{\infty}\frac{x^{\alpha}}{x^{n}+1}dx & =\frac{1}{n}\int_{0}^{\infty}\frac{y^{\frac{\alpha}{n}+\frac{1}{n}-1}}{y+1}dy\cmt{y=x^{n}}\\ & =\frac{1}{n}\int_{1}^{0}z\left(\frac{1-z}{z}\right)^{\frac{\alpha+1}{n}-1}\left(-\frac{1}{z^{2}}\right)dz\cmt{z=\frac{1}{y+1},y=\frac{1-z}{z},dy=-\frac{1}{z^{2}}dz}\\ & =\frac{1}{n}\int_{0}^{1}z^{-\frac{\alpha+1}{n}}\left(1-z\right)^{\frac{\alpha+1}{n}-1}dz\\ & =\frac{1}{n}B\left(1-\frac{\alpha+1}{n},\frac{\alpha+1}{n}\right)\\ & =\frac{1}{n}\Gamma\left(1-\frac{\alpha+1}{n}\right)\Gamma\left(\frac{\alpha+1}{n}\right)\\ & =\frac{\pi}{n}\sin^{-1}\left(\frac{\left(\alpha+1\right)\pi}{n}\right) \end{align*} \]ページ情報
| タイトル | 分母分子にxのべき乗を含む積分 |
| URL | https://www.nomuramath.com/rrzz84hu/ |
| SNSボタン |
3角関数と3角関数の対数の積分
\[
\int\sin\left(z\right)\log\left(\sin z\right)dz=-\cos z\log\sin z+\cos z+\log\left(\sin\frac{z}{2}\right)-\log\left(\cos\frac{z}{2}\right)+C
\]
(*)分母に1乗と2乗ルートの積分
\[
\int\frac{1}{\left(z+\alpha\right)\sqrt{z^{2}+\beta}}dz=\frac{\tanh^{\bullet}\left(\frac{\alpha z-\beta}{\sqrt{\alpha^{2}+\beta}\sqrt{\beta+z^{2}}}\right)}{\sqrt{\alpha^{2}+\beta}}
\]
分母分子にべき乗があり分母には定数が足されている定積分
\[
\int_{0}^{\infty}\frac{x^{a}}{c+x^{b}}dx=\frac{c^{\frac{a+1}{b}-1}}{b}\pi\sin^{-1}\left(\frac{a+1}{b}\pi\right)
\]
分母に2乗のルートがある積分
\[
\int\frac{1}{\sqrt{z^{2}+\alpha}}dz=\frac{\sqrt{\alpha}\sqrt{\frac{z^{2}}{\alpha}+1}}{\sqrt{z^{2}+\alpha}}\sinh^{\bullet}\frac{z}{\sqrt{\alpha}}+C
\]

