Linked Questions
52 questions linked to/from Lesser-known integration tricks
7 votes
1 answer
280 views
Closed-form of $\int_0^{\pi/2} \arctan(x)\cot(x)\,dx$
I'm looking for a closed-form of the following integral problem. $$I = \int_0^{\pi/2} \arctan(x)\cot(x)\,dx.$$ The numerical approximation of $I$ is $$I \approx 0....
2 votes
1 answer
267 views
Using variation of parameters to solve $y''-25y=x$
I keep trying to solve this but I end up needing to do integration by parts like 3 or 4 times. My only question is, is that going to be the only way to do this? If so it will literally take me hours. ...
0 votes
2 answers
96 views
Is there a way to solve $\int \frac1{(x^2+a^2)^2}$ without $x=\tan t$ substitution?
This is from an integral problems book, it is a part of the solution of a larger problem. $$\int_0^1\frac1{(x^2+4)^2}~dx=\frac18\Biggl( \Bigl(\frac x{x^2+4} \Bigr) \bigg\vert _0^1~+~\int_0^1\frac{dx}{...
1 vote
1 answer
240 views
Integrate $(x^n)\sin x$, where $n$ is an arbitrary natural number
I know how to integrate, for example $x^2\sin x$ via integration by parts. But how would one approach $x^n\sin x$, where $n$ is an arbitrary natural number? Do I have have to use integration by parts $...
4 votes
2 answers
177 views
How to evaluate $\int \frac1{(x^2+a^2)^{m}}dx$
The integral $$\int\frac{1}{(x^2+a^2)^m}dx$$ can be expressed by a recursive formula of $$\frac{1}{2a^2(m-1)}\frac{x}{(x^2+a^2)^{m-1}} + \frac{2m-3}{2a^2(m-1)}\int\frac{dx}{(x^2+a^2)^{m-1}}$$ I do not ...
0 votes
3 answers
214 views
How to solve the integral of $\frac 1{(x^2+1)^2}$
I need to evaluate $$ \int_0^1 \dfrac 1{(x^2+1)^2}. $$ I was absent for this lecture and I'm sort of lost on where to go. I set $x = \tan (\theta)$ and $dx = \sec^2(\theta)\, d\theta$. And this ...
0 votes
4 answers
120 views
Integration by parts to find volume
I am integrating $$\pi\int\left(\cfrac{1}{x^2+4}\right)^2dx$$ I understand I need to integrate by parts. But why is it that $$u=\cfrac{1}{x^2+4}$$ and not $$u=\left(\cfrac{1}{x^2+4}\right)^2$$ How ...
1 vote
1 answer
85 views
How to integrate $\frac{dx}{(x^2+k^2)^m}$, with $m$ positive integer.
How can I integrate: $$\int \frac{1}{(t^2+k^2)^m}\, dt$$ without trygonometric substituition? where $t= (x+(p/2))$ and $k= (1-(p^2/4))$ coming from an equation with complex roots: $x^2 + px + q.$ ...
0 votes
1 answer
95 views
A misleading integration step.
Compute $$\int_{-\pi/2}^{\pi/2} \frac{x^2\cos(x)}{1+e^x}$$ The first step itself given in the solution is changing $e^x$ to $1/e^x$ . Now as first step is making no sense to me so I didn't post the ...
1 vote
3 answers
118 views
Definite integral on $[0,\pi]$ [closed]
How to calculate the following integral if $\varepsilon \in (0,1)$: $$\int \limits_{0}^{\pi}\frac{d\varphi}{(1+\varepsilon\cos \varphi)^2}$$
0 votes
4 answers
88 views
Is there a way to evaluate $\int \frac{\text{d}x}{x^2(x^2+1)^2}$ without partial fractions or substitution?
I would like to know if there is an algebraic way to evaluate $$\int \frac{\text{d}x}{x^2(x^2+1)^2}$$ Without using partial fraction decomposition and without substitution. My attempt is something ...
1 vote
1 answer
160 views
The general problem of finding $\int \frac{dx}{(ax^2 + bx + c)^2}$ [closed]
I know that $\displaystyle\int \dfrac1{ax^2+bx+c}\,\mathrm dx$ is easily solvable using completing the square, but my question is how would would find $$\displaystyle\int\frac{1}{\left(ax^2+bx+c\...
1 vote
2 answers
152 views
Hard Integral $\int{\frac{3x+4}{(x^2+5)^2}dx}$ without Partial Fraction Decomposition
So I was trying to use partial fraction decomposition on this problem, and I realized that it didn't work, as it is already in partial fraction decomposition form. $$\int{\frac{3x+4}{(x^2+5)^2}dx}$$ ...
0 votes
2 answers
85 views
Am I calculating the integral $\int x^2 \cos x\> dx $ correctly?
I need to calculate: $$\int x^2 \cdot \cos{x} \cdot dx $$ My step by step solution: Using the formula: $$\int udv=uv-\int vdu$$ $\color{gray}{\boxed{\color{black}{\int x^2 ⋅ \cos{x}⋅ dx=x^2 \sin{x}-...
1 vote
1 answer
159 views
How to prove $\int_0^{2\pi} f(a+rcos(x),b+rsin(x)) dx =2{\pi}f(a,b)$?
Recently I've been looking around for integral tricks here, here, and here (just to name a few). I came across the post on brilliant's website here (move the slider/ scroll down to the very bottom to ...