For questions related to usage of Wolfram Alpha.

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0
votes
1answer
40 views

stuck with a cubic equation

I picked an equation $0= x^3 +x^2 -2x -1$ I plotted it with geogebra, to see if it had more than $1$ real root. It definitely cuts the $x$-axis $3$ times. But when I checked wolfram alpha, to see ...
3
votes
2answers
38 views

Real integral getting numerically evalued to complex number

I tried feeding th following integral into WolframAlpha: $$\int_0^2\frac{1}{3\sqrt{x}(\log(x))^{\frac13}},$$ to get an idea of its value. Result: http://bit.ly/strangeint ...
7
votes
5answers
87 views

$\sec\theta$ never equals $\tan\theta$. Or does it?!?

Wolfram-alpha is disagreeing with me. I am wondering why: which of us is wrong? I was writing a question to demonstrate why domains of functions matter. The question is: Does there exist an angle ...
1
vote
1answer
56 views

Wolfram interpretation of arccot(x)

I was calculating a $$\lim_{{x \to -\infty}}\left(\frac{4-x}{1-x}\right)^{2x\mathrm{arccot}(x)}$$ and found a problem og how wolframalpha presents $\mathrm{arccot}(x)$. I was taughted that plot of ...
2
votes
3answers
83 views

Wolfram alpha error in global minimization?

Let us consider the function $$f(x,y)= x + y^2 - \ln(x+y)$$ If you try to minimize it using Wolfram Alpha (http://www.wolframalpha.com/input/?i=minimize+x%2By%5E2-ln%28x%2By%29), it founds a local ...
3
votes
1answer
29 views

Curvature of plane curve, formula disagrees with Mathematica?

I have the following equation $$y=\pi\ln(2x)$$ And when I ask Mathematica/WolframAlpha for the curvature I get $$K=\frac{\pi x}{(x^2+\pi^2)^{3/2}}$$ However the formula for curvature of a plane ...
4
votes
3answers
96 views

How does Wolfram Alpha come up with the substitution $x = 2\sin u$? Integration/Analysis

I have to integrate $$ \int_0^2 \sqrt{4-x^2} \, dx $$ I looked at the Wolfram Alpha step by step solution, and first thing it does is it substitutes $x = 2\sin(u)\text{ and } \,dx = 2\cos(u)\,du$ ...
1
vote
1answer
53 views

Torricelli's Law with a Sphere (Ignore Mathematica part, already solved)

Edit 1: According to this PDF, second page. The differential equation for a hemisphere becomes $$(r^2h-h^2) h' = -a^2\sqrt{2gh}$$ This differs from the equation I got, which looks like: ...
7
votes
3answers
741 views

Integration substitution: How does Wolfram Alpha come up with this step?

I have to integrate $$ \int \frac{1}{(\sin x) (\cos x)} \, dx $$ I looked at the Wolfram Alpha step by step solution to figure out how to do it. First, it rewrites the integral as: $$ \int (\csc ...
0
votes
1answer
19 views

Laplace Transform of $e^t\cos(3t)\operatorname{heaviside}(t)$

Find the Laplace Transform of $e^t \cos(3t) \operatorname{heaviside}(t)$ Since $\operatorname{heaviside}(t)g(t) = \mathcal{L}(g(t)) $ and $\mathcal{L}(e^t\cos(3t)) = \frac{(s-1)}{(s-1)^2+9} $ ...
1
vote
2answers
46 views

compute exponential of matrix with wolfram alpha

I would like to use wolfram alpha to compute matrix exponential. I have tried with the exponential of the identity matrix, with this input: exp({{1,0},{0,1}}) But what I get is unexpected. The ...
0
votes
1answer
39 views

Solution to h'(t) = h(t)^j : Wolfram Alpha mistake?

This should be a quick and easy one. Trying to teach myself a bit more about differential equations, so I put the following equation into Wolfram Alpha: $$h'(t) = h(t)^j$$ It gave me the following ...
0
votes
2answers
42 views

Solve system of equations

Are there any good resources for solving systems of equations out there? I tried to put this into wolfram alpha, but it doesn´t seem to work: ...
1
vote
1answer
33 views

Evaluating a decimal exponent

The example I am stuck with is $(-1)^.456$. According to my calculator, the answer is -1. According to WolframAlpha and the Google Calculator, it is a complex number. WolframAlpha -- ...
1
vote
0answers
62 views

Did Wolfram Alpha make this term up?

So I'm currently taking a Trigonometry class and I'm using the iOS version of the Wolfram-Alpha app to assist me with some of the more mundane calculations (Pythagorean Theorem, etc) and I've come ...
0
votes
1answer
75 views

how to substitute a variable by a number in wolframalpha

Peace be upon you, How can I compute \begin{align*} sin'(0) \end{align*} in Wolframalpha? like what in Maple, I try subs(diff(sin(x),x),x=0) But it doesn't ...
0
votes
0answers
159 views

using wolfram alpha to solve a system of nonlinear differential equations

Will Wolfram Alpha solve a system of nonlinear differential equations with initial values and graph the solutions? Essentially, I want to hand Wolfram a first-order system with variables x_1, x_2, ...
0
votes
1answer
56 views

How can the integral of $|\sin(x)|$ be $-\cos(x)\text{sgn}(\sin(x))$?

Wolfram|Alpha tells me that $\int|\sin(x)| = -\cos(x)\text{sgn}(\sin(x))$ (which happens to also be its derivative), but I don't understand how this is possible, because the resulting function jumps ...
0
votes
2answers
54 views

Simplifying fractional exponents

I am very confused about the following: whenever I put in into wolfram alpha the answer it gives me is "indeterminate", is it not possible to simplify fractional exponents or something? if the ...
0
votes
0answers
31 views

Plotting Dirichlet Series $L_{\tau}(s)$ related to Ramanujan tau function in Mathematica

According to wikipedia, Ramanujan tau function $\tau:\mathbb{N}\to\mathbb{Z}$ is defined by equating the coefficients of the power series on both sides of the identity: ...
0
votes
1answer
42 views

Name of special function used used by Wolfram integrator

Integrating $\frac{e^{-r}}{(\sqrt{2t-r})}$ with respect to $r$ between $r=t$ and $r=2t$ on Wolfram (http://www.wolframalpha.com/widgets/view.jsp?id=8ab70731b1553f17c11a3bbc87e0b605) gives the answer ...
0
votes
2answers
38 views

How do I get wolfram to solve this problem?

I am trying to check some answers and can't seem to get wolfram to work properly. I type in the following command : integrate x.sin(x) dx and it doesn't provide any solution it just says "visual ...
1
vote
1answer
79 views

Is there any way how I can use Mathematica in Introduction Logic course?

I am very new comer to Wolfram Mathematica software tool and I am interesting is there any way how I can apply this tool for Introductory Logic course. I am participating at the course on 'coursera' ...
0
votes
0answers
126 views

Why is Wolfram Alpha wrong?

I calculated $$\tan 75^o - [\cos 13^o\cdot \cot 23^o \cdot \tan 31^o \cdot \tan 35^o\cdot \tan41^o]$$ and I got a nonzero answer: ...
1
vote
0answers
22 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
38 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
65 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 ...
3
votes
3answers
416 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
vote
1answer
59 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
votes
2answers
172 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
43 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
votes
3answers
66 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.
1
vote
1answer
95 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
vote
1answer
51 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
vote
2answers
254 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
112 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
47 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
211 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
111 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
29 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
172 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
63 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
vote
1answer
149 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
vote
1answer
40 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
42 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
114 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 ...
0
votes
1answer
49 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 Alpha™ ...
0
votes
0answers
148 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? ...
0
votes
2answers
123 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
98 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 ...