Concerns all aspects of integration, including the integral definition and computational methods. For questions solely about the properties of integrals, use in conjunction with (indefinite-integral), (definite-integral), (improper-integrals) or another tag(s) that typically describe(s) the types of ...

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0
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1answer
20 views

solve $(x^2 y+y)dy/dx =\arctan(x)$ , $y(1) = -1$

solve the equation $(x^2 y+y)(dy/dx) = \arctan(x)$ , $y(1) = -1$ my work until now $(x^2 y+y)\,dy = \arctan(x)\,dx$ $x^2 y\,dy+y\,dy = \arctan(x)\,dx$ ---> stuck here
1
vote
2answers
18 views

Integral Question using the Rule of Subsitution

I'm confused as to why $ \int e^{kx} $ = $ \frac {e^{kx}}{k} + C$. I'm using the rule of substitution and came to the conclusion that it should be $ e^{kx}k $ because the derivative of $kx$ is $k$. ...
0
votes
0answers
22 views

Gradient and Laplacian in integral.

Let $u,v,f$ be functions of $\mathbb{R}^n$ to $\mathbb{R}$, with compact support in a domain $U$, this formula $$\int_{U} f(x) (Du \cdot Dv) dx = \int_{U} f(x)(u D(Dv)) dx = \int_{U} f(x) u(x) \Delta ...
0
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0answers
29 views

Calculate integral

I have to calculate $$\operatorname{PV}\int_{-\infty}^{\infty}\frac{1}{\pi}\frac{y}{1+y^2}dy$$ I ended up with ...
0
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0answers
14 views

Using polar coordinates in this integral

I'm trying to solve something along the lines of: $$\iint \frac{\partial F_1(x,y)}{\partial x}+\frac{\partial F_2(x,y)}{\partial y}dydx$$ which I want to change to polar coordinates, but I don't ...
2
votes
4answers
50 views

integration $\int_{0}^{3}(12/(x^2 -6x+12))\,dx$

$$\int_{0}^{3} \frac{12}{x^2 - 6x + 12} \,dx$$ I assume that $x^2 - 6x + 12 = (x-3)^2 + 3$, then $t = x - 3 \rightarrow dt = dx$ since $$\int_{0}^{3} \frac{12}{t^2 + 3}\,dt$$ and now I am stuck. ...
1
vote
0answers
47 views

Feynman Integration Problem

$$ I = \frac{\pi^2}{8} - \int_0^1 \frac{\arctan(x)}{\sqrt{1-x^2}} \,dx $$ Evaluate $I$ $$ I = \frac{\pi^2}{8} - \int_0^1 \frac{\arctan(x)}{\sqrt{1-x^2}} \,dx$$ $$f(a) = \int_0^1 ...
3
votes
2answers
42 views

$\int \frac{\exp (z)(\sin(3z)}{(z^2-2)(z^2)} dz$ on $|z|=1$

So I need to calculate \begin{equation*} \int \frac{\exp(z) \sin(3z)}{(z^2-2)z^2} \, dz~\text{on}~|z|=1. \end{equation*} So I have found the singularities and residues and observed that the ...
0
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0answers
23 views

Can limits to definite integral be vectors?

There are two cases: 1-Limits are scalar and function to be integrated is vector. 2- Limits are vector and function to be integrated is vector. Are both valid. If yes can you give example for each. ...
2
votes
1answer
21 views

Calculating volume by shell integration

$y = \ln x$, region is delimited by $y = -1$, $y = 2$ and the $y$-axis, it rotates around the $y$-axis. It's quite simple to solve by using disk integration but I can't get it right with shell ...
0
votes
2answers
58 views

Why does $\int_0^{\infty}e^{-\frac{z^2}{4}}dz=\sqrt{\pi}\ $?

Why does $$\int_0^{\infty}e^{-\frac{z^2}{4}}dz=\sqrt{\pi}$$ How do you get there from the standard integral which equals $\sqrt{2\pi}$ ?
1
vote
2answers
43 views

Given $|f(x)|=1$,how to construct an $f(x)$, such that $\int ^{+\infty }_{0}f\left( x\right) dx$ converges

Here's the problem: Given $|f(x)| = 1$, construct an $f(x)$, such that $$\int ^{+\infty }_{0}f\left( x\right) dx$$ converges. I think this problem may be done by dividing the 1s and -1s smartly, but ...
0
votes
1answer
18 views

Trying to integrate the volume of a body

I was trying to integrate the volume of a body blocked by $z=0$, $z=2x$, $x+y=3$ and $y=0$ using the double integral... but I don't really know how to approach this.
1
vote
3answers
35 views

A really basic integration question concerning differentials

I'm really, really confused with this. Please, please help me. $$$$ My Calculus teacher taught me that the integral symbol and the differential with respect to which we are integrating are like ...
1
vote
0answers
30 views

Integration of a symmetric function

I have a bit of confusion about the following situation. Let's assume that we have a symmetric function $f(x,y)$ where it has the property $f(x,y) = f(y,x)$ for all $x$ and $y$. $x$ and $y$ have the ...
0
votes
2answers
38 views

Volume by double or triple integral?

I was trying to integrate the volume of a body blocked by $z=0,\; z=2x,\; x+y = 3$ and $y=0$ using the double integral... however it didn't work yet. I'm convinced its a double integral and not a ...
0
votes
2answers
36 views

Can you explain this equation to someone who hasn't learned integration?

So I have just entered 11th grade and started limits on my own but my Physics textbook has an equation which I don't understand, I suspect it uses integration which I haven't learned yet. So can ...
2
votes
1answer
61 views

A necessary condition to $F'(x)=f(x)$ for a continuous function $f$

Theorem: Consider , $$F(x)=\int_a^xf(t)\,dt$$ If the function $f:[a,b]\to \mathbb R$ is continuous then $F(x)$ is differentiable and $F'(x)=f(x).$ I know that the continuity condition ...
2
votes
1answer
52 views

Calculating $\int_0^\pi \frac{1}{a+b\sin^2(x)} dx $

How do I calculate this integral? $a \gt b$ is given. $$\int_0^\pi \frac{1}{a+b\sin^2(x)} dx $$ I am confused since WolframAlpha says one the one hand, that $F(\pi) = F(0) = 0 $ , but with some ...
-3
votes
2answers
38 views

Differential equations/ 4 [on hold]

How to solve this differential equation: $$ \frac{ydy+zdz}{\sqrt{y^2+z^2}}+\frac{ydz-zdy}{y^2}=0$$ I gave similar but then nothing happens maybe this is exact differential equations?
0
votes
1answer
27 views

Partial derivatives after a change of variables

Say I have a function of $n$ variables $F(x_{1}, x_{2}, x_{3},...,x_{n})$, where $x_{1} = g_{1}(y_{1}, y_{2}, y_{3},...,y_{m})$, $x_{2} = g_{2}(y_{1}, y_{2}, y_{3},...,y_{m}),\dots, x_{n} = ...
2
votes
1answer
43 views

Verify solution to ODE

I am given the ODE $$\left(f''(x)+\frac{f'(x)}{x} \right) \left(1+f'(x)^2 \right) = f'(x)^2f''(x)$$ and I already know that the solution to this ODE is given by $$f(x)= c \cdot arcosh \left( ...
-1
votes
1answer
64 views

How do I calculate $ \int_{-\infty}^{\infty} e^{-ax^2} \;\mathrm{d}x$ for $a>0 $ [duplicate]

$$ \int_{-\infty}^{\infty} e^{-ax^2} \;\mathrm{d}x \quad\text{for } a>0 $$ I don't even know where to begin to be honest so I haven't made any progress on it. The answer is $\sqrt{\pi/a}$. Is ...
0
votes
0answers
18 views

solution uniqueness of non-linear Fredholm equations

the equation is $F(x)=G(\int k(x,y)f(y)dy)$ $(*)$ where $f(x)=dF(x)/dx$ is the unknown and it's required to be non-negative. With integral by parts we'll have the form of a non-linear Fredholm ...
1
vote
1answer
24 views

Cartesian to Spherical Coordinates

Can someone help me passing this triple integral from cartesian to spherical coordinates ? Thanks in advance ;) ...
0
votes
1answer
48 views

Questions about integration

I'm still a bit confused about definite integration although got the basic idea of how to do integration. The problem is to integrate functions on a uniform distribution over [50, 150]. Firstly ...
-1
votes
0answers
29 views

first-order nonlinear ordinary differential equation0 [on hold]

How to solve this differential equation: $$(x^{2}+\ln(y))\cos(2x)+\sin(2x)(xdx+\frac{dy}{2y})=0 $$ I tried to rearrange the equation to the form $\frac{dy}{dx}$ but I couldn't.
0
votes
2answers
57 views

integration substitution what am I doing wrong?

integrate $\frac{x^3}{(4+x^2)}$ Let $u = 4+x^2$ so $\frac{du}{2}=xdx$ Then I need to integrate $\frac{(u-4)}{u}$ which comes out as $u-4\ln u$ converting back to $x$, $4+x^2-4 \ln(4+x^2)+C$ But I ...
-2
votes
2answers
71 views

$\int _{ 0 }^{ 1 }{ \frac { { x }^{ t }-1 }{ \ln { x } } dx } $ [duplicate]

How do I solve the following integral: $$\int _{ 0 }^{ 1 }{ \frac { { x }^{ t }-1}{ \ln { x } } dx } $$
3
votes
2answers
62 views

Finding line that divides an area into equal halves.

My question is simple, but I am not getting the answers for some reason. The question is: Consider the area enclosed between the graph of $y = 1 - x^2 $and the $x$ axis. Which line parallel to the ...
0
votes
0answers
28 views

Volume integral $\int_V y \frac{dy}{dt} + z\frac{dz}{dt} dV$

How do I solve $$\int_V y \frac{dy}{dt} + z\frac{dz}{dt} dV$$ Where $V$ is the volume of a hollow sphere. Usually I would use spherical coordinates, but I don't know how to express $\frac{dy}{dt} $ ...
1
vote
1answer
11 views

Finding the surface integral of a scalar field through an implicitly defined surface

What is the best method of trying to find the surface integral of a scalar field over a certain surface $\Sigma$ that's only defined as being the part of one surface which is cut off by another ...
0
votes
0answers
18 views

Given a set of points, find the plane parallel to plane $p$ where your plane cuts the area in half.

Given a set of point $G=\{(x,y,z) | 0 \le x\le2, 0 \le y \le 2, 0 \le z \le xy\}$ for all $x,y>0$ Find the plane $p$ parallel to plane $zy$ whereas you get two areas equal in size What I did was ...
1
vote
2answers
21 views

Derivation of second moment of area of a circle, a small question

I hope this question will be allowed on math.stackexchange, as the question is a mathematical one even though the subject might be from engineering. I am trying to derive the formula for the second ...
0
votes
1answer
33 views

Taking the partial derivative of an integral

Can I simply take the integral of this function with respect to $t$ by bringing the differential operator under the summation? $$u(x,t)=\int_{-\infty}^{\infty} ...
0
votes
1answer
37 views

Solving the integral $\int_{-\infty}^{\infty} (1+x^2)^{-3/2}$ with $\sinh$, $\cosh$?

I want to solve the following integral: $$\int_{-\infty}^{\infty} (1+x^2)^{-3/2}$$ I thought maybe it's possible with $\sinh$ or $\cosh$ or something similar, but I can't figure it out. Thanks in ...
0
votes
1answer
33 views

Integration of a triple integral

Evaluate the integral $$\int_{z=0}^4\int_{y=0}^1\int_{x=2y}^2{cos(x^2)\over \sqrt{z}}dxdydz$$ by changing the order of integration.
2
votes
3answers
48 views

How do I go about solving the integral of csc x?

So here is a solution provided by another user a couple of years ago and I've seen this solution before but I'm not clear on how or why? What would make me think or tip me off that I should multiply ...
6
votes
2answers
394 views

Integrating over the naturals. What does it mean?

Let $F$ be the power set of $\Bbb{N}$ and consider the measurable space $(\Bbb{N}, F)$. Then what does it mean to take the integral with respect to the measure $\mu(A) = \sum_{a \in A} \frac{1}{a}$. ...
-1
votes
0answers
31 views

Solving $\frac{\partial}{\partial r} \int_r^x g(y,r) dy = -\frac{\cosh(a\sqrt{x^2-r^2})}{\sqrt{x^2-r^2}}$

I am stuck on this problem. I need to find the correct function, $g(y,r)$, such that $$ \frac{\partial}{\partial r} \int_r^x g(y,r) dy = -\frac{\cosh(a\sqrt{x^2-r^2})}{\sqrt{x^2-r^2}} $$ So far I am ...
2
votes
4answers
147 views

How to evaluate this indefinite integration $\int \frac{\tan^4 \theta d \theta}{1-\tan^2 \theta}$?

I have to solve this indefinite integration $$\int \frac{\tan^4 \theta d \theta}{1-\tan^2 \theta}$$ I tried it as follows $$I=\int\frac{(\sec^2 \theta-1)\tan^2 \theta d \theta}{1-\tan^2 ...
-1
votes
6answers
88 views

integrate $1/(x(x^2-1)^{1/2})$

$$\int\frac{1}{x (x^2-1)^{1/2}} \, dx=\text{ ?}$$ Hi! I'm new to the website and I didn't learn math in English so I may make mistakes with terminology. I have given a math homework and it says the ...
3
votes
2answers
90 views

use parseval's identity to evaluate the integral $ \int_{-\pi}^{\pi}\sin^4 xdx$

use parseval's identity to evaluate the integral \begin{equation} \int_{-\pi}^{\pi}(\sin x)^4dx\end{equation} I'm familiar with Parseval's identity which states that for each piecewise continuous ...
7
votes
2answers
140 views

Feynman technique of integration for $\int^\infty_0 \exp\left(\frac{-x^2}{y^2}-y^2\right) dx$

I've been learning a technique that Feynman describes in some of his books to integrate. The source can be found here: ...
0
votes
1answer
116 views

How to solve this integral: $\int \frac{\sqrt{-x^2 - x + 2}}{x^2}dx$?

Question is self explanatory. I have an exam and our professor gave us questions. This is the one I couldn't do. Any ideas would be very helpful: $$\int \frac{\sqrt{-x^2 - x + 2}}{x^2}dx$$
0
votes
0answers
35 views

double integral to consecutive integrals

can someone explain to me how was this step done? I have little knowledge about this area of mathematics, as much as i can say the double integral of a function F over an area X is constructed by this ...
-4
votes
2answers
50 views

Calculate $\int_{0}^{1} \frac{x^3}{\sqrt{1+x^4}}dx$ [on hold]

Help with this integral, please! $$\int_{0}^{1} \frac{x^3}{\sqrt{1+x^4}}dx$$
6
votes
1answer
131 views

Integration of $\frac{e^{\cos^2x}+\ln(1+x)}{10^{x^3}\arctan(\sqrt{x})}$, possibly numerical

A couple of days ago I came across the following integral: $$\int_{0.02}^{0.08} \frac{e^{\cos^2x}+\ln(1+x)}{10^{x^3}\arctan(\sqrt{x})}\,{\rm d}x$$ The funny thing is, I found this integral written in ...
0
votes
2answers
41 views

Integrating $\sin^3(x)/(2+\cos(x))$

I could use some help solving the following integral: $$\int \frac{\sin^3(x)}{2+\cos(x)} dx$$ So far I tried using the equality: $$\sin^3(x) = \frac{3}{4} \sin(x) - \frac{1}{4}\sin(3x)$$ which ...
1
vote
1answer
60 views

Evaluating $ \int_0^\theta \cosh(a\sin x) dx$

The integral below seems quite simple, but I couldn't find anywhere the result. $$ I = \int_0^\theta \cosh(a\sin x) dx$$ I tried to expand it into Taylor expansion series and successfully evaluate the ...