2
votes
1answer
35 views

Inverse trig and trigh in integration?

I have just done part (iii) of this question and can get the right answer but am a bit confused why do we take arcosh i.e. just the principle value of cosh and not the other value. I presume this is ...
0
votes
1answer
34 views

Find a linear combination of $u_n$'s satisfying $u(x,1) = \sin(2\pi x) -\sin(3\pi x)$

I have the following problem: $$u_n(x,y) = \sin(n\pi x)\sinh(n\pi y), \;\;\;n = 1, 2, 3, ...$$ Find a linear combination of the $u_n$'s that satisfies: $$u(x,1) = \sin(2\pi x) -\sin(3\pi x)$$ Any ...
1
vote
1answer
36 views

Finding the derivative of $\;\operatorname{arccoth}(\sin x)$

I have tried to solve it but I don't why it's wrong. I need to take the derivative of $\;\operatorname{arccoth}(\sin x)$: By using chain rule, I get: $$\dfrac 1{1 - \sin^2 x}\cdot \cos x = \dfrac ...
0
votes
2answers
79 views

How to integrate this $\frac{1}{(1-e^{2x})^{1/2}}$?

Please how to integrate this $$\frac{1}{(1-e^{2x})^{1/2}}$$ I have tried $u= e^x$ But I think that is wrong So can anyone help me ?
0
votes
1answer
62 views

Why ${\rm arcosh}(\cosh x) =x $?

I'd like to know why ${\rm arcosh}(\cosh x) =x$. Also I have read that the derivative of ${\rm arcosh}(\cosh x) = \sinh x/|\sinh x|$. Why? Thanks all
0
votes
1answer
63 views

Find $x$ if $\sinh(x)=2$

I want to know how to find $x$ if $\sinh(x)=2$. I already know that $\sinh(x) = \dfrac{e^x -e^{-x}}{2}$. Hence, $$\frac{e^x -e^{-x}}{2} = 2 \implies e^x -e^{-x}=4$$ but I don't know what should I do ...
0
votes
1answer
67 views

When I choose arctanh or arccoth?

I want to know When I choose $\operatorname{arctanh}$ or $\operatorname{arccoth}$ ? E.x $$\int_0^3 \frac{1}{49-4x^2} dx$$ It will be $(1/14) \operatorname{arctanh} (2x/7)$ or $(1/14) ...
1
vote
2answers
95 views

The derivative of $\tanh x$

I'm trying to calculate the derivative of $\displaystyle\tanh h = \frac{e^h-e^{-h}}{e^h+e^{-h}}$. Could someone verify if I got it right or not, if I forgot something etc. Here goes my try: ...
2
votes
3answers
78 views

What is wrong? Symmetric function

I need some advice here. What is $y(\ln(4))$ if the function $y$ satisfies: $$\frac{dy}{dx} = 1-y^2$$ and is symmetric about the point $(\ln(9),0)$. Solving that equation I end up with: ...
2
votes
0answers
220 views

Parametric Equation of a Hyperbolic Paraboloid

I need to make two trace plots of the hyperbolic paraboloid $z=x^2-y^2$. In the first plot, we set $z$ equal to a constant $k$, $z=k$. How do I find the parametric equation for this representation of ...
5
votes
1answer
150 views

A conjecture $\int_{-\infty}^\infty\frac{\arctan e^x}{\cosh x}\cdot\frac{\tanh\frac{x}2}{x}dx\stackrel?=\frac\pi2\ln2$

I need to find a closed form for this integral: $$\mathcal{I}=\int_{-\infty}^\infty\frac{\arctan e^x}{\cosh x}\cdot\frac{\tanh\frac{x}2}{x}dx.$$ A numerical integration results in an approximation ...
13
votes
3answers
263 views

Closed form for $\int_{-\infty}^\infty\operatorname{sech}(x)\operatorname{sech}(a\, x)\ dx$

Let $$f(a)=\int_{-\infty}^\infty\operatorname{sech}(x)\operatorname{sech}(a\, x)\ dx,$$ where $\operatorname{sech}(z)=\frac2{e^z+e^{-z}}$ is the hyperbolic secant. Here are values of $f(a)$ at some ...
-3
votes
1answer
93 views

How to simplify this equation?

How to simplify this equation? I know that: $\sin^2 p+\cos^2 p = 1$ But how to go further?
2
votes
2answers
90 views

proving that the differences of squares of hyperbolic sin/cos is an integer.

The hyperbolic sine and cosine are defined as following: $\sinh(x)=\dfrac{e^x-e^{-x}}{2}$ $\cosh(x)=\dfrac{e^x+e^{-x}}{2}$ How do I show that their differences of squares are always an integer for ...
1
vote
1answer
52 views

Hyperbolic integration solving

$$ \therefore x-x_0 = \pm \int_{\phi(x_0)}^{\phi(x)} \frac{d \phi}{\sqrt\frac{\lambda}{2}\left( \phi^2-(\frac{m}{\sqrt \lambda})^2\right)} $$ How can we write the above equation to as, $$ \phi(x) = ...
33
votes
2answers
410 views

Closed form for $\prod_{n=1}^\infty\sqrt[2^n]{\tanh(2^n)},$

Please help me to find a closed form for the infinite product $$\prod_{n=1}^\infty\sqrt[2^n]{\tanh(2^n)},$$ where $\tanh(z)=\frac{e^z-e^{-z}}{e^z+e^{-z}}$ is the hyperbolic tangent.
2
votes
1answer
74 views

definite Integration

A integration is given, $$M = \int_{- \infty}^{\infty} \left[\frac{1}{2} \left(\frac{d\phi}{dx}\right)^2 + \frac{\lambda}{4}(\phi^2-v^2)^2\right] dx,$$ where $$m=v\sqrt\lambda$$ and $$ \phi(x)= ...
3
votes
4answers
89 views

Hyperbolic cosine

I have an A level exam question I'm not too sure how to approach: a) Show $1+\frac{1}{2}x^2>x, \forall x \in \mathbb{R}$ b) Deduce $ \cosh x > x$ c) Find the point P such that it lies on ...
6
votes
3answers
380 views

Show $\sum_{n=1}^{\infty}\frac{\sinh\pi}{\cosh(2n\pi)-\cosh\pi}=\frac1{\text{e}^{\pi}-1}$ and another

Show that : $$\sum_{n=1}^{\infty}\frac{\cosh(2nx)}{\cosh(4nx)-\cosh(2x)}=\frac1{4\sinh^2(x)}$$ $$\sum_{n=1}^{\infty}\frac{\sinh\pi}{\cosh(2n\pi)-\cosh\pi}=\frac1{\text{e}^{\pi}-1}$$
0
votes
1answer
38 views

For the previous question on hypergeo function

For $\displaystyle\int_0^{\infty}x^n\frac{\sinh ax}{\cosh bx}\text{d}x$, $\left|a\right|<b$ I think we can evaluate $\displaystyle\int_{0}^{\infty }{{{\text{e}}^{cx}}\frac{\sinh ax}{\cosh ...
2
votes
1answer
256 views

A hard integral with hyperbolic function

I was self studying integral. I meet a difficult problem here: $$\int_{0}^{\infty }{{{x}^{n}}\frac{\sinh ax}{\cosh bx}}\text{d}x=\frac{\pi }{2b}\cdot \frac{{{\text{d}}^{n}}}{\text{d}{{a}^{n}}}\tan ...
4
votes
4answers
161 views

Evaluating $\int_0^1 x \sinh (x) \ \mathrm{dx}$

I am looking to evaluate $$\int_0^1 x \sinh (x) \ \mathrm{dx}$$