For questions related to usage of Wolfram Alpha.

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1answer
25 views

Wolfram Mathematica: Find constants in ODE solution?

Let's say, I have a general solution to some ODE, e.g. y(x)=x+c, and a condition y(0) = 5. I want to type in something like Solve[{y[x]=x+c, y[0] =5}, {c}] and get the value of a constant. Is there a ...
0
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2answers
49 views

Is there a way to rewrite integrals in Mathematica using u substitution?

In Mathematica, can I give it an integral and a few substitution rules and have it rewrite the integral in terms of those variables?
1
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0answers
17 views

radius of convergence of $1/\ln(in)$

I have series when $n$ goes from $1$ to infinity $(z/\ln(in))^n$ and need to find the radius of convregence. I tried this $1/R = \limsup ((1/\ln(in))^n)^(1/n)$ when $n \to \infty$ (Cauchy's rule), ...
1
vote
1answer
21 views

How to do reduce rows with Wolfram Alpha over certain set

If I want to row reduce a matrix: $$ \begin{matrix} 1 & -1 & 0 & 4 \\ 2 & -2 & 1 & 3 \\ 5 & -5 & 1 & 15 \\ \end{matrix} $$ ...
0
votes
1answer
31 views

Count of possible hands math + Python vs Wolfram Alpha

So I wanted to write a Python program to calculate some probabilities using hyper geometric distributions. However, I seem to get probabilities over 1 sometimes, so there must be something wrong with ...
0
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1answer
32 views

How is this root simplified [closed]

As seen on wolfram Alpha. I factored out 3^2, how is the further simplification done? Particularly how and why was 2/69 gotten in the radical. ...
3
votes
3answers
389 views

Wolfram|Alpha returns the wrong result: how can I solve this “high precision” equation?

$$1-(1-1.40*10^{-36})^x \ge 1.09*10^{-9}$$ I want to estimate $x$ such that the probability on the left becomes larger than the probability on the right. A solution must exist because ...
1
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1answer
46 views

Why is a complex number plus infinity equal to infinity?

Why is $$2 + 3 i + \infty = \infty$$ according to Mathematica and Wolfram Alpha? Shouldn't it be: $$2 + 3 i + \infty = \infty + 3 i$$ ? After all: $$2 + 3 i + 10 = 12 + 3 i$$ and not: $$2 + 3 i ...
6
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2answers
148 views

A strange answer for $\int _{-1}^1 \log x\; dx$

I typed $\int _{-1}^1 \log x\; dx$ on Wolfram Alpha. It is giving the answer to be $-2+i\pi$. Can someone please explain what is happening?
0
votes
1answer
30 views

Order of operations on Wolfram Alpha

I am confused by the fact that on Wolfram Alpha x(2)/x(2) = 1 but 2(x)/2(x) = x^2. Could someone explain what rules are being ...
0
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3answers
51 views

Parametrization of curve

I need to find parametrization of $(1+x)y^2=(y+2x)x$. I tried to put all $x$-s on one side, and all $y$-s on other but that can't be done. Could someone please help? Thanks.
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1answer
54 views

Wolfram Alpha “Rule of Three” [closed]

Regarding WolframAlpha what is the correct input for the following statement?: If X=Y Then 2X=?
1
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1answer
21 views

Plotting the intersection of multiple surfaces with WolframAlpha

I want to plot the intersection of two surfaces like in this post. But if I enter the much simplified expression ContourPlot3D[{x^2 + y^2 + z^2 - 4=0, xy=1}, {x, -2, 2}, {y, -2, 2}, {z, -2, 2}] ...
1
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1answer
44 views

How to use Wolfram|Alpha to calculate Friday the 13ths

I know someone born on the 13th and we were talking about how Friday the 13th is his birthday from time to time. I thought that might be a good question for Wolfram|Alpha but no matter how I phrase it ...
1
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2answers
79 views

Wolframalpha find Fourier series

Is there a way to write down the following in Wolframalpha? $$f(x)=\begin{cases}1-x,& 0\leqslant x\leqslant 1\\ 0,&1\lt x\leqslant2\end{cases}.$$
3
votes
3answers
106 views

Why is $\frac{\sum_{n=1}^{\infty} n}{\sum_{n=1}^{\infty} n}$ indeterminate?

We all know that $\dfrac{f(x)}{f(x)} = 1$ (where $f(x) \neq 0$) and that $\sum_{n=1}^{x} n = \dfrac{x(x+1)}{2}$. So, given $f(x) \stackrel{\text{def}}{=} \sum_{n=1}^{x} n$, we show that ...
3
votes
0answers
44 views

Strange things on WolframAlpha: derivation, modulo and doubling result

I asked WA what is the derivative of $\frac1{\cos((x \bmod \pi/2)-\pi/4))}$ equal to for $x=0$. A very strange result came out. The exact result is $-\sqrt2 \mathsf{Mod}^{(1,0)}(0,\frac\pi2)$, ...
2
votes
2answers
62 views

Solve an equation for a particular variable using Wolfram Alpha

I want to express variable from equation in WolframAlpha web. I tried several keywords but it didn't work. For example I have equation $$y=x+z+k,$$ and I want Wolfram to rewrite it for variable $x$, ...
4
votes
3answers
97 views

How does WolframAlpha simplify sine and cosine?

When I feed WolframAlpha an expression like $\sin({\pi\frac{2}{3}})$, it correctly prints that this is equal to $\frac{\sqrt3}{2}$, instead of the decimal expansion $0.866025403\ldots$. Perhaps it ...
0
votes
2answers
22 views

Polar graph inWolfram alpha

Maybe do you know wolfram alpha which draw graph Bu I cannot draw polar graph. For instance $$r=2\cos\ (t)\ : x^2+y^2=r^2=2r\cos\ t=2x\ (circle)$$ If we enter this, then it show $cosine$ graph, not ...
-1
votes
3answers
83 views

Symmetric matrix 10 x 10

Can You give me the example of symmetric matrix 10 x 10. Or if You know online symmetric matrix generator then give me the links. I tried to make this with Wolfram Mathematica but I did not find a ...
2
votes
1answer
56 views

The curve $(\cos(\sin x),\sin(\cos x))$ as plotted by Wolfram Alpha

I've just gotten this from Wolfram Alpha: It makes no sense to me. $\cos(\sin x)$ is never zero so how can this curve cross the $y$-axis?
1
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1answer
66 views

Computing 2d radially symmetric Fourier transforms (with Wolfram Alpha)

Let's assume that I "know" $\mathcal{F}\{\operatorname{circ}(r)\}(\rho)=\frac{J_1(2\pi\rho)}{\rho}$ $\mathcal{F}\{(1-r^2)\operatorname{circ}(r)\}(\rho)=\frac{J_2(2\pi\rho)}{\pi\rho^2}$ because I ...
1
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1answer
37 views

Wolfram Exponential Fit not match as formulas

I am using WolframAlpha Exponential-Fit formulas to find equation of Exponential Regression http://mathworld.wolfram.com/LeastSquaresFittingExponential.html but after implementation, I tested with a ...
0
votes
1answer
40 views

Problem with graphing a function.

To my understanding, function $f(x)=\frac{1+x}{1+x^3}$ should not be defined with $x=-1$ since: $f(-1)=\frac{1+(-1)}{1+(-1)^3}=\frac{1+(-1)}{1+(-1)}=\frac{0}{0}$ However, Google's plot drawer and ...
2
votes
1answer
87 views

Using newthon method to find nth root - did wolframalpha get it wrong?

I'm trying to implement the n-th root algorithm as outlined here: http://en.wikipedia.org/wiki/Nth_root My code however, takes a lot of iterations (more than 100) to converge. I tried to check with ...
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1answer
42 views

How does one provide a determinant as input to Wolfram Alpha?

$\begin{vmatrix} 17&-12&4&0\\ 5&9&-2&1\\ 3&-6&-1&14\\ 11&7&0&8\\ \end{vmatrix}$ How would one express the preceding determinant in the Wolfram Alphaâ„¢ ...
0
votes
0answers
49 views

What do Root[], #, & mean in Wolfram Alpha?

I wanted to find the roots of a particular equation by using Wolfram Alpha. What I get are strange answers. Thay look like this: What do all the symbols there mean and what does the whole thing mean? ...
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2answers
52 views

“Which is equivalent for restricted x values to”

I've been checking my homework via Wolfram Alpha, and for several questions (example below) in this section (trigonometric integrals). I'd be correct up until the last step, in which Wolfram Alpha ...
3
votes
1answer
91 views

What are these numbers?? (floor(a)=0)

I was just so I decided to go and look up the roots of floor(a) in WolframAlpha where a is any number, real or complex, and of course the interval [0,1) showed up as an answer but I also got these ...
2
votes
2answers
64 views

Behavior of $f(x) = \sum_{n=1}^x \frac{1}{n}$

I plotted the function $$f(x) = \sum_{n=1}^x \frac{1}{n}$$ in Wolfram Alpha over $x\in\mathbb{R}$ and it gave me some unexpected behavior for negative $x$. This function is obvious for ...
1
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1answer
156 views

Evaluation of the integral $\int_{-6}^{-3}\frac{\sqrt{x^2-9}}{x}$

How to evaluate the following integral? I have tried the following things but I have no idea to continue after the last step. Moverover, the integral seems wrong when compared with the ans from ...
2
votes
1answer
103 views

Can wolfram alpha compute symbolic vector derivatives

Can Wolfram alpha be used to find out say $$\nabla_x\left(\|y-Ax\|_2\right)$$ What command do I use? I tried some obvious ways, and googled a bit, but didn't find anything.
0
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3answers
116 views

Wolfram Derivation Error

I'm trying to derive the equation $$y = (2x-6)^4$$ I thought that it would be $$\frac{dy}{dx} = 8(2x-6)^3$$ Wolframalpha says $dy/dx = 64(x-3)^3$ Who's correct? I thought it would be a simple ...
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votes
3answers
79 views

How to solve that kind of equation using Wolfram Mathematica? [closed]

I need to find all variables $$A, B, C, D$$ for given equation with independent variable $$s$$ How can Mathematica solve that? Example, not working: UPDATE: One Two Three Four ...
1
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1answer
42 views

Please explain the steps in the solution of this integral

After unsuccessfully solving an integral, I turned to WRA for some guidance. Unfortunately, I don't understand what happen in the solution. More particularly, I don't understand why the numerator has ...
0
votes
0answers
304 views

Wolfram and solids of revolution

I'm looking for the easiest method of having WolframAlpha calculate the volume of a solid of revolution. I've been working on a particular Project Euler problem for a long time. So far, I think I ...
1
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1answer
43 views

Discrepancy over matrix exponential

I am trying to compute $\large e^A$ for $A = \left( \begin{array}{ccc} 0 & a \\ 0 & 0 \end{array} \right)$ Using $\large e^A = \sum \limits_{k=0}^\infty \frac{1}{k!} A^k$ Writing out the ...
0
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1answer
96 views

Why WolframAlpha gives different results?

Any idea why WolframAlpha gives different answers when computing the indefinite integral of these functions with respect to x first or with respect to y first? ...
0
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0answers
56 views

How are massive parametric functions that make a picture (example inside) created?

[Here's] (http://www.wolframalpha.com/input/?i=sergey+brin+curve) an example of what I'm talking about. The equation might take a second to load. How are these generated, computer algorithms? I ...
4
votes
0answers
113 views

Proof that cos(1) is transcendental?

So, I was playing around on Wolfram|Alpha (as we nerds like to do) and it said cos(1) was transcendental. Could someone provide me with the proof that cos(1) is transcendental?
0
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1answer
37 views

Help with creating formula

Lets say I have colony of 100 bacteria's. Within 1 year, each of bacteria brings up a "child" and becomes "infertile". After next year, children of bacteria bring up "children" and becomes ...
0
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1answer
58 views

Finding vertex of a parabola -conflicting answers

For a given problem $g(x) = 5x^2 - 2x +1$, we were expected to describe the graph. WolframAlpha and I are finding conflicting issues. I do not think I made an approximation anywhere that would explain ...
2
votes
1answer
32 views

Change linear plot to 100% plot in Wolfram Alpha

Recently I have used this input for WolframAlpha: Plot (forumla1), (formula2), (formula3), {a, 0, 50} It's generating "Linear Plot" like on picture on left. Is ...
1
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1answer
53 views

Is there an analitical solution for such ODE $$ \frac{d y(x)}{dx}=\frac{a*y(x)^3+b}{c* y(x)^3+ d} $$

I have an ODE $$ \frac{d y(x)}{dx}=\frac{a*y(x)^3+b}{c* y(x)^3+ d} $$, $$a,b,c,d - const$$ And I would love to solve it analitically. I tred maple 15 and 17 and got $$ y \left( x \right) =1/2\,{ ...
0
votes
1answer
50 views

What is DifferenceRoot?

In a question I asked earlier today in an effort to simplify the equation on the left below, I was pointed toward Wolfram Alpha. I got this back: I honestly have no idea what the right half of ...
1
vote
3answers
70 views

Trigonometric inequality bounded by lines

How can it be shown that $$16x\cos(8x)+4x\sin(8x)-2\sin(8x)<|17x|?$$ This problem arises from work with damped motion in spring-mass systems in Differential Equations. I have gotten to this ...
4
votes
3answers
130 views

Inverse Function (and WolframAlpha gives different Result)

I wanted to calculate the inverse function of $$ f(x) = \frac{1}{x} + \frac{1}{x-1} $$ Quite simple I thought, put $$ y = \frac{1}{x} + \frac{1}{x-1} = \frac{2x-1}{x(x-1)} $$ rearrange and solve $$ ...
1
vote
1answer
51 views

Calculating the eigenvalues of a given matrix, please check my results

Given the matrix $$A = \left(\begin{array}{ccc} 1&-0.85&0\\ 1.7&-1&0\\ 0 & 0.85 & 4 \end{array}\right)\in\mathbb{C}^{3\times3}$$ I am now looking for the ...
0
votes
1answer
94 views

Specifying complex domain in Wolfram Alpha

Hopefully this kind of question is ok, have seen a couple of other WA-queries that hasn't been downvoted. Apologies if not. I'm trying to find the max/min of a complex function over certain domains, ...