Reducing an explicit integral to beta function values

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Using Euler integrals, calculate the integral.

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(1)

∫02dxx2(2−x)3\int_{0}^{2} \frac{d x}{\sqrt[3]{x^{2}(2-x)}};

(2)

∫−12dx(2−x)(1+x)34\int_{-1}^{2} \frac{d x}{\sqrt[4]{(2-x)(1+x)^{3}}};

(3)

∫−22dx(2+x)3(2−x)4\int_{-2}^{2} \frac{d x}{\sqrt[4]{(2+x)^{3}(2-x)}};

(4)

∫02dxx3(2−x)25\int_{0}^{2} \frac{d x}{\sqrt[5]{x^{3}(2-x)^{2}}};

(5)

∫12(2−x)2(x−1)3dx\int_{1}^{2} \sqrt[3]{(2-x)^{2}(x-1)} d x;

(6)

∫03dxx3(3−x)35\int_{0}^{3} \frac{d x}{\sqrt[5]{x^{3}(3-x)^{3}}}.

Using Euler integrals, calculate the integral.

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(1)

∫12x−12−xdx(x+3)2\int_{1}^{2} \sqrt{\frac{x-1}{2-x}} \frac{d x}{(x+3)^{2}};

(2)

∫011−xxdx(x+2)2\int_{0}^{1} \sqrt{\frac{1-x}{x}} \frac{d x}{(x+2)^{2}};

(3)

∫01dx(x+1)x2−x33\int_{0}^{1} \frac{d x}{(x+1) \sqrt[3]{x^{2}-x^{3}}};

(4)

∫01xdx(2−x)x2(1−x)3\int_{0}^{1} \frac{x d x}{(2-x) \sqrt[3]{x^{2}(1-x)}};

(5)

∫01⋅x(1−x)⋅dx\int_{0}^{1} \cdot \sqrt{x(1-x)} \cdot d x;

(6)

∫01x(1−x)34(x+1)3dx\int_{0}^{1} \frac{\sqrt[4]{x(1-x)^{3}}}{(x+1)^{3}} d x

Using Euler integrals, calculate the integral.

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(1)

∫0+∞dx1+x3\int_{0}^{+\infty } \frac{d x}{1+x^{3}};

(2)

∫0+∞x4(1+x)2dx\int_{0}^{+\infty } \frac{\sqrt[4]{x}}{(1+x)^{2}} d x;

(3)

∫0ax2a2−x2dx\int_{0}^{a} x^{2} \sqrt{a^{2}-x^{2}} d x;

(4)

∫−∞+∞xex/2e2x+1dx\int_{-\infty }^{+\infty } \frac{x e^{x / 2}}{e^{2 x}+1} d x;

(5)

∫0+∞xα−11+xβdx,0<α<β\int_{0}^{+\infty } \frac{x^{\alpha -1}}{1+x^{\beta }} d x, 0 < \alpha < \beta

(6)

∫01x1−α(1−x)α(x+1)3dx,−1<α<2\int_{0}^{1} \frac{x^{1-\alpha }(1-x)^{\alpha }}{(x+1)^{3}} d x,-1 < \alpha < 2.

Using Euler integrals, calculate the integral.

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(1)

∫0+∞xα−1(1+x)2dx,0<α<2\int_{0}^{+\infty } \frac{x^{\alpha -1}}{(1+x)^{2}} d x, 0 < \alpha < 2;

(2)

∫0+∞xp+1(1+x2)2dx,−2<p<2\int_{0}^{+\infty } \frac{x^{p+1}}{\left(1+x^{2}\right)^{2}} d x,-2 < p < 2;

(3)

∫0π/2tg⁡αx(sin⁡x+cos⁡x)2dx,0<α<1\int_{0}^{\pi / 2} \frac{\operatorname {tg}^{\alpha } x}{(\sin x+\cos x)^{2}} d x, 0 < \alpha < 1;

(4)

∫01x1−x33dx\int_{0}^{1} x \sqrt[3]{1-x^{3}} d x;

(5)

∫01x2nx(1−x2)3dx,n∈N\int_{0}^{1} \frac{x^{2 n}}{\sqrt[3]{x\left(1-x^{2}\right)}} d x, n \in N;

(6)

∫0+∞xdx(1+x3)2\int_{0}^{+\infty } \frac{x d x}{\left(1+x^{3}\right)^{2}};

(7)

∫0+∞x2α−11+x2dx,0<α<1\int_{0}^{+\infty } \frac{x^{2 \alpha -1}}{1+x^{2}} d x, 0 < \alpha < 1;

(8)

∫0π/2sin⁡4xcos⁡6xdx\int_{0}^{\pi / 2} \sin^{4} x \cos^{6} x d x;

(9)

∫0π/2tg⁡2α−1xdx,0<α<1\int_{0}^{\pi / 2} \operatorname {tg}^{2 \alpha -1} x d x, 0 < \alpha < 1.

Express the integral in terms of values of the beta function.

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(1)

∫01dx1−xαn,α>0\int_{0}^{1} \frac{d x}{\sqrt[n]{1-x^{\alpha }}}, \alpha > 0;

(2)

∫01xα(1−xβ)γdx,α>−1,β>0,γ>−1\int_{0}^{1} x^{\alpha }\left(1-x^{\beta }\right)^{\gamma } d x, \alpha > -1, \quad \beta > 0, \quad \gamma > -1;

(3)

∫0axα−1(a−x)β−1dx,a>0,α>0,β>0\int_{0}^{a} x^{\alpha -1}(a-x)^{\beta -1} d x, \quad a > 0, \quad \alpha > 0, \quad \beta > 0;

(4)

∫0+∞xα−1(1+x)βdx,0<α<β;\int_{0}^{+\infty } \frac{x^{\alpha -1}}{(1+x)^{\beta }} d x, 0 < \alpha < \beta ;

(5)

∫01x3α1−x33dx,α>−13\int_{0}^{1} \frac{x^{3 \alpha }}{\sqrt[3]{1-x^{3}}} d x, \quad \alpha > -\frac{1}{3};

(6)

∫0+∞xα(a+bxβ)pdx,a>0,b>0,β>0,0<α+1β<p\int_{0}^{+\infty } \frac{x^{\alpha }}{\left(a+b x^{\beta }\right)^{p}} d x, a > 0, \quad b > 0, \quad \beta > 0, \quad 0 < \frac{\alpha +1}{\beta } < p.

Express the integral in terms of values of the beta function.

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(1)

∫0πsin⁡px1+cos⁡xdx,p>1\int_{0}^{\pi } \frac{\sin^{p} x}{1+\cos x} d x, \quad p > 1;

(2)

∫0π/2sin⁡α−1xcos⁡β−1x(sin⁡x+cos⁡x)α+βdx,α>0,β>0\int_{0}^{\pi / 2} \frac{\sin^{\alpha -1} x \cos^{\beta -1} x}{(\sin x+\cos x)^{\alpha +\beta }} d x, \alpha > 0, \beta > 0

(3)

∫0π/2sin⁡2α−1xcos⁡2β−1x(a2sin⁡2x+b2cos⁡2x)α+βdx,α>0,β>0,a>0,b>0\int_{0}^{\pi / 2} \frac{\sin^{2 \alpha -1} x \cos^{2 \beta -1} x}{\left(a^{2} \sin^{2} x+b^{2} \cos^{2} x\right)^{\alpha +\beta }} d x, \quad \alpha > 0, \quad \beta > 0, a > 0, \quad b > 0;

(4)

∫0π/2sin⁡α−1xcos⁡α−1x(a2sin⁡2x+b2cos⁡2x)αdx,α>0,ab>0\int_{0}^{\pi / 2} \frac{\sin^{\alpha -1} x \cos^{\alpha -1} x}{\left(a^{2} \sin^{2} x+b^{2} \cos^{2} x\right)^{\alpha }} d x, \quad \alpha > 0, \quad a b > 0;

(5)

∫0π/2sin⁡αxcos⁡βxdx,α>−1,β>−1\int_{0}^{\pi / 2} \sin^{\alpha } x \cos^{\beta } x d x, \quad \alpha > -1, \quad \beta > -1;

(6)

∫0πsin⁡α−1x(1+βcos⁡x)αdx,0<∣β∣<1,α>0\int_{0}^{\pi } \frac{\sin^{\alpha -1} x}{(1+\beta \cos x)^{\alpha }} d x, \quad 0 < \left|\beta \right| < 1, \quad \alpha > 0;

(7)

∫−11(1+x)2α−1(1−x)2β−1(1+x2)α+βdx,α>0,β>0\int_{-1}^{1} \frac{(1+x)^{2 \alpha -1}(1-x)^{2 \beta -1}}{\left(1+x^{2}\right)^{\alpha +\beta }} d x, \quad \alpha > 0, \quad \beta > 0;

(8)

∫ab(x−a)α(b−x)β(x+c)α+β+2dx,0<a<b,c>0,α>−1,β>−1\int_{a}^{b} \frac{(x-a)^{\alpha }(b-x)^{\beta }}{(x+c)^{\alpha +\beta +2}} d x, \quad 0 < a < b, \quad c > 0, \quad \alpha > -1, \quad \beta > -1.

Prove the equality:

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(1)

∫01dx1−x4=Γ2(1/4)42π\int_{0}^{1} \frac{d x}{\sqrt{1-x^{4}}} = \frac{\Gamma^{2}(1 / 4)}{4 \sqrt{2 \pi }};

(2)

∫0πdθ3−cos⁡θ=14πΓ2(14)\int_{0}^{\pi } \frac{d \theta }{\sqrt{3-\cos \theta }} = \frac{1}{4 \sqrt{\pi }} \Gamma^{2}\left(\frac{1}{4}\right) (Hint. Set cos⁡θ=1−2x)\cos \theta = 1-2 \sqrt{x});

(3)

∫0π(sin⁡θ1+rcos⁡θ)α−1dθ1+rcos⁡θ=2α−1(1−r2)α/2[Γ(α/2)]2Γ(α),∣r∣<1\int_{0}^{\pi }\left(\frac{\sin \theta }{1+r \cos \theta }\right)^{\alpha -1} \frac{d \theta }{1+r \cos \theta } = \frac{2^{\alpha -1}}{\left(1-r^{2}\right)^{\alpha / 2}} \frac{[\Gamma (\alpha / 2)]^{2}}{\Gamma (\alpha )},\left|r\right| < 1

(Hint. Set tg⁡θ2=1+r1−rx\operatorname {tg} \frac{\theta }{2} = \sqrt{\frac{1+r}{1-r}} \sqrt{x});

(4)

∫01dx1−x4∫01x2dx1−x4=π4\int_{0}^{1} \frac{d x}{\sqrt{1-x^{4}}} \int_{0}^{1} \frac{x^{2} d x}{\sqrt{1-x^{4}}} = \frac{\pi }{4};

(5)

∫0+∞e−x4dx∫0+∞x2e−x4dx=π82\int_{0}^{+\infty } e^{-x^{4}} d x \int_{0}^{+\infty } x^{2} e^{-x^{4}} d x = \frac{\pi }{8 \sqrt{2}};

(6)

∏k=1n∫0+∞xk−1e−xndx=(1n)n−1/2(2π)(n−1)/2\prod_{k = 1}^{n} \int_{0}^{+\infty } x^{k-1} e^{-x^{n}} d x = \left(\frac{1}{n}\right)^{n-1 / 2}(2 \pi )^{(n-1) / 2}

(Hint. Use the reflection formula (4) and the equality zn−1z−1=∏k=1n−1(z−e2kπi/n)\frac{z^{n}-1}{z-1} = \prod_{k = 1}^{n-1}\left(z-e^{2 k \pi i / n}\right).

Express in terms of values of the Γ\Gamma-function and the B\mathrm{B}-function the integrals:

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(1)

∫0∞∫0∞(x+y)pe−x−ydxdy,p>0\int_{0}^{\infty } \int_{0}^{\infty }(x+y)^{p} e^{-x-y} d x d y, p > 0

(2)

∫0∞∫0∞(x2+y2)pe−x2−y2dxdy,p>−1\int_{0}^{\infty } \int_{0}^{\infty }\left(x^{2}+y^{2}\right)^{p} e^{-x^{2}-y^{2}} d x d y, p > -1;

(3)

∫0∞∫0∞∫0∞e−(x2+y2+z2)pdxdydz,p>0\int_{0}^{\infty } \int_{0}^{\infty } \int_{0}^{\infty } e^{-\left(x^{2}+y^{2}+z^{2}\right)^{p}} d x d y d z, p > 0

(4)

∬G(x2+y2)p(1−x2−y2)qdxdy,p>−1,q>−1,G={x>0,y>0,x2+y2<1}\iint_{G}\left(x^{2}+y^{2}\right)^{p}\left(1-x^{2}-y^{2}\right)^{q} d x d y, p > -1, q > -1, G = \left\{ x > 0, y > 0, x^{2}+y^{2} < 1\right\};

(5)

∭Gdxdydz(t2−x2−y2−z2)p,p<1,G={x2+y2+z2<t2}\iiint_{G} \frac{d x d y d z}{\left(t^{2}-x^{2}-y^{2}-z^{2}\right)^{p}}, p < 1, G = \left\{ x^{2}+y^{2}+z^{2} < t^{2}\right\}.

References

[ККЧ+03] Кудрявцев Л.Д., Кутасов А.Д., Чехлов В.И., Шабунин М.И. Функции многих переменных. 2-е изд., ФИЗМАТЛИТ, 2003.