For questions related to usage of Wolfram Alpha.

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6
votes
3answers
1k views

Derivative of floor function

I thought the derivative of function $\text{floor}(x)$ should be $\infty$ for integer values of $x$ and 0 elsewhere. But wolframalpha plot showed something different. Is there any explanation?
1
vote
2answers
5k views

Wolfram Alpha: How to define constants in a system of equations?

I'd like to use WA to solve a small system of nonlinear equations, that involve both constants and the variables of interest. How do I "tell" WA which variables are the constants, and which are the ...
1
vote
1answer
264 views

Moving the negative out of the integral - a bug in Wolfram Alpha?

A guy I follow on Twitter seems to be having some issues with Wolfram Alpha - namely that moving a negative outside of an integral results in two different answers: $\int -f(x) = -\int f(x)$ gives ...
26
votes
4answers
999 views

A limit wrong using Wolfram Alpha

I want to calculate the following limit: $$\displaystyle{\lim_{x \to 0} \cfrac{\displaystyle{\int_1^{x^2+1} \cfrac{e^{-t}}{t} \; dt}}{3x^2}}$$ For that, I use L'Hopital and the Fundamental Theorem ...
0
votes
1answer
35 views

How to calculate HarmonicNumber(x, 1.6)?

I got this solution while using Wolframalpha: $$ (-1.66667 n+1/2-0.133333/n+0.0208/n^3-0.0127573/n^5+O((1/n)^6))/n^1.6+2.28577 $$ Could somebody tell me this solution step-by-step? I need to write ...
0
votes
1answer
749 views

WolframAlfa/Mathematica how to find function local maximum on interval

I have a polynomial function and i want to find it's minimum and maximum on a the interval [0, 5] with Wolfram Alphaa but i forgot the proper input. I recall it went something like so: $x^4 + x^3 + ...
5
votes
4answers
156 views

Should $x=-2$ be included as an answer for $\frac{x^2+8x+12}{x^2+5x+6}>0$?

$$\frac{x^2+8x+12}{x^2+5x+6}>0$$ First of all while solving inequalities I need to check domain so in this case $$x^2+5x+6\neq0$$ $$x\neq-2,\ x\neq-3$$ Later on ...
2
votes
1answer
323 views

Circumference of the ellipse, elliptic integrals, and WolframAlpha

The arc length of a graph of a function $f(x)$ is $$\mathcal{l} = \int_a^b \sqrt {1 + f'(x)^2} dx$$ If you choose $f$ to be a parametrization of the ellipse with $a=1, b=\frac{1}{2}$, i.e. $f(x) = ...
1
vote
1answer
497 views

Wolfram|Alpha Plotting multiple geometric objects

I am trying to use WoflramAlpha to plot several gemoetries at once. It works fine up to an extent but after I add three different geometries to draw it just says it doesn't understand and picks ...
2
votes
2answers
162 views

(Wolframalpha) this shouldnt give x=50?

This is my problem: I need x or y for the triangle area that forms between the vertical axis(y) and the function y=100+2x where the area is equal to 2500. so I used for condition to the linear ...
7
votes
1answer
613 views

Wrong Wolfram alpha result?

I have this function $$ f(x,y) = \left\{ \begin{array}{ll} \frac{x^3}{x^2 + y^2} & \mbox{if } (x,y) \neq (0,0) \\ 0 & \mbox{if } (x,y) = (0,0) \end{array} \right. $$ And I want to ...
24
votes
1answer
352 views

Iterated exponent of $i$

WolframAlpha seems to tell me that $e^{e^{e^{e^{e^{e^{e^{e^{e^{e^{e^i}}}}}}}}}} = 1$, see link. Is this just an error or is it for real? Adding one more $e$ to the bottom of the tower gives me the ...
3
votes
1answer
264 views

How can I construct a 2^63-gon with a straightedge and compass?

I entered 2^63 as a stand alone value at WolframAlpha. Among the responses was a factoid that 'A regular 9223372036854775808-gon is constructible with a straightedge and compass.' What is such a ...
0
votes
1answer
60 views

Confusion in the answers given by mathematica

When I typed in 6^-1 mod 49 in Wolfram|Alpha, it gave me an answer of 41. Link here If I type the same thing as (1/6) mod 49 , I don't see 41 any more. Why is this happening ?Link here A ...
1
vote
1answer
382 views

How to plot and shade on Wolfram Alpha?

Many Mathematica parameters don't work on Wolfram Alpha. I tried filling -> f which it does not recognize. I am trying to plot a simple region bounded by $y = ...
4
votes
2answers
136 views

Is $2^{\log_2(-5)}$ defined?

As far as I know for $\log_2 x$ to be defined $x$ must be higher than 0. However when I enter $2^{\log_2(-5)}$ into wolframalpha it gives result $-5$. Is it mistake?
4
votes
1answer
5k views

Contour integration and wolfram

I am not sure if this is the right site to ask this question, but here it is: Does Wolfram Alpha do contour integrals? If so how might I access that feature. Also, is there an online manual for ...
1
vote
1answer
110 views

Question on y axis of Gamma probability distribution

Afternoon. I'm looking into using the Gamma (Erlang) distribution for a certain quantity that I need to model. I noticed by plugging in some values for the distribution parameters that the y axis ...
1
vote
1answer
80 views

Trivial transfiguration

I have $\frac{2ab}{ab-ac-bc+c^2}$. Of course it's $\frac{2ab}{c^2-ac-bc+ab}$ which is $\frac{2ab}{c^2-c(a+b)+ab}$ but for the latter Wolfram tells me it's not the same as $\frac{2ab}{ab-ac-bc+c^2}$. ...
2
votes
3answers
627 views

WolframAlpha blows simple substitution?

I am to find a formula for the n-th derivative of $$\frac{1+x}{1-x}$$ I came up with $$\frac{(-1)^{n+1} \times 2 \times n!}{(1-x)^{n+1}}$$ This seems right, but I noticed that WolframAlpha somehow ...
0
votes
1answer
438 views

How to calculate vertices of dodecahedron using W|A?

Can I calculate for example with wolfram alpha coordinates of vertices of dodecahedron? I know coordinates of center point of dodecahedron (center of gravity) and the height of dodecahedron. Thanks ...
2
votes
1answer
308 views

Is wolframalpha a good nonlinear optimization tool? [closed]

Also how do you restrict the domain to be integers in wolfram alpha?
0
votes
3answers
226 views

Why doesn't WolframAlpha factor my equation?

I entered in a simple-looking quadratic equation, expecting WA to factorize it for me, but then it gives me all this other stuff without the actual factors. The result is exactly the same as my input. ...
1
vote
2answers
4k views

Why does Wolfram Alpha handle $\log$ and $\ln$ the same?

I thought $\log(n)$ was like $100^x = n$ and $\ln(n)$ was $e^x = n$. But when I do $\ln(80)$, it gives me the answer for $\log$. Why is that?
0
votes
1answer
14k views

Taylor series expansion of arctan(x) around the point 0

This is actually a technical question about why I'm getting different results when trying to do the same thing using Maxima and WolframAlpha. When I enter expand arctan(x) in WolframAlpha I ...
0
votes
1answer
496 views

Priority of parentheses and brackets in basic arithmetic.

Wolfram alpha is giving inconsistent results to this problem: When I enter: 16÷2( 8-3(4-2) )+1 the result is 17. When I enter: 16÷2[ 8-3(4-2) ]+1 the result is 5. and 16÷2*[ 8-3(4-2) ]+1 brings ...
1
vote
1answer
1k views

Set of modular equations in Wolfram|Alpha

Am I able to solve set of modular equations in Wolfram|Alpha, like for example: $ \left\{\begin{matrix} x \equiv 2 \pmod{3} \\ x \equiv 3 \pmod{5} \end{matrix}\right. $ ?
1
vote
1answer
112 views

An integral evaluation

I tried my luck with Wolfram Alpha, with $p \in \mathbb{R}$ $$\int_{-\infty}^{\infty} \frac{x^p}{1+x^2} dx = \frac{1}{2} \pi ((-1)^p+1) \sec(\frac{\pi p}{2})$$ for $-1<p<1$, and doesn't exist ...
0
votes
1answer
114 views

Help me with this mock-long-division $\frac{-x+2}{x^{2}+x-2}=\frac{-4}{3(x+2)}+\frac{1}{3(x-1)}$

$$\frac{-x+2}{x^{2}+x-2}=\frac{-4}{3(x+2)}+\frac{1}{3(x-1)}$$ Wolphram Alpha states that one can do this with long division, I cannot immediately realize it. Could someone show the trick to simplify ...
1
vote
1answer
181 views

p-norm of series / Mathematica

When computing the $p$-norm of the series $x_n = \mathrm e^{\mathrm i n}$ for $n \in \mathbb{Z}$ (not $\mathbb{N}$), the sum should not converge: $$\|x\|_p^p = \sum_{n \in \mathbb{Z}} (\mathrm ...
1
vote
2answers
273 views

Graph of a Log Function

I am curious as to why Wolfram|Alpha is graphing a logarithm the way that it is. I was always taught that a graph of a basic logarithm function $\log{x}$ should look like this: However, ...
2
votes
1answer
2k views

How to type logical expressions in WolframAlpha?

Usually WolframAlpha understands what logical expression I have entered but sometimes I can't find a way to do it especially when you are using equivalent sign. For example if I have $$ p \land q ...
10
votes
1answer
627 views

How would you input xkcd.com/287 into WolframAlpha?

In this XKCD comic, a stick figure asks an NP-complete problem to order exactly 15.05 worth of appetizers out of a menu that includes the following list of prices: ...
4
votes
2answers
14k views

Using Wolfram Alpha For Solving A System Of Equations

How do i input the below system of equations in wolfram alpha in order to solve for the unknowns and plot them? If i just say "solve" and input these equations one after the other with a simicolen ...
3
votes
3answers
3k views

Using Wolfram Alpha to output table of values over the integers

I'm trying to get Wolfram Alpha to output a table of values over the integers for a given function, in example: n^2-n 1----1 4----2 9----3 ... ... (using '-'s instead of ...
1
vote
1answer
189 views

How to graph a cumulative subtraction on Wolfram Alpha

I'd like to graph a timing algorithm that I'd been using (that did essentially the opposite of what I wanted). I apologize if I'm not using the correct name to refer to it. Essentially it was timer = ...
0
votes
2answers
534 views

Have I found a bug in Wolfram Alpha's Partial Derivative Solver?

I was using This Wolfram Alpha Page to calculate the partial derivatives of the sum of two gaussians. It believes the answer to be: $$ e^{-(b-x)^2/2 c^2} $$ but the working shows it as ending on: ...
0
votes
2answers
801 views

a question about the sum of $ e^{ikx}$

I have a simple question. Let $ S = \sum\limits_{k = 1}^n {e^{ikx} } $ using the typical trick , we also have $ S\left( {e^{ix} - 1} \right) = e^{i\left( {n + 1} \right)x} - e^{ix} $ and if $ ...
6
votes
1answer
736 views

How do I plot multi case function in wolfram or geogebra?

How do I plot the following multi case function in wolfram or geogebra? $$ \begin{eqnarray*} f(x) = \begin{cases} 1, &\text{if }x \text{ is an integer}, \\ 0, &\text{if }x \text{ is ...
2
votes
1answer
231 views

Problems Using Wolfram Alpha

I've always had some problem with the usage of wolfram alpha.It computes simple derivates, integrals and solves simple linear and quadratic equations flawlessly.It seems to me that it ignores step by ...
0
votes
1answer
201 views

Understanding a Wolfram|Alpha explanation on a simple integral

I'll probably kick myself when someone explains it, but I can't understand where the 1/12 comes from after the re-substitution of u? I thought it would be 1/3, but it clearly isn't. Why is that? ...
0
votes
1answer
13k views

Use WolframAlpha to compute the real Fourier series of a function

How can I use Wolfram|Alpha to compute the Fourier series (with real coefficients $a_0, a_n$ and $b_n$)? (The 'Fourier series' command seems to summon the complex series) I.e. $f(x) = x + \pi$ for ...
8
votes
1answer
2k views

variable bounds on definite integrals in Wolfram|Alpha

I often have trouble getting Wolfram|Alpha to compute definite integrals with variable bounds, and I'm wondering whether I'm missing something. Some examples: $\int_a^b \sin x\mathrm dx$ and $\int ...
3
votes
0answers
198 views

How to Create a Lesson Plan with Wolfram Alpha

This will be my first post in this forum. I am so excited to see a lot of interesting posting from the community. From the FAQ, I learned that Mathematics stack exchange discussed about mathematical ...
4
votes
1answer
694 views

Is Wolfram Alpha Wrong? (LU Decomposition)

Ok, I've been working on a matrix solver for a while (no, its not going well, thanks for asking), and just discovered something that worrys me alot; The problem at hand is LU Decomposition of a ...
10
votes
2answers
28k views

How to type logarithms in Wolfram|Alpha?

Its sometimes hard to type it if logarithm is not natural and base is not 10, especially if base is variable. So anyone know rules how to type?
2
votes
2answers
686 views

limit of $2^n/3^{n/2}$ as $n\to\infty$

$$ \lim_{n\to\infty}\frac{2^n}{3^{n/2}}$$ I used wolfram to get the limit as follows: "lim n tends infinity 2^n/3^(n/2)". And using L'Hospital's rule the result was: ...
13
votes
2answers
373 views

What is the meaning of a number's “representation” on Wolfram Alpha?

When searching a number on Wolfram Alpha, one of the results is its representation. For example, for 8549: 8549 has the representation 8549 = $5·2^6·3^3-91$. Similarly for 75290: ...
2
votes
2answers
680 views

Comparing integral resolutions using Wolfram Alpha / Mathematica

Equations are in $\LaTeX$ format; I'm still trying to understand how MathJax works. Given the following integral: $\int_0^{+\infty } \frac{1}{x \sqrt{x}} \, dx$ I'm pretty sure that does not ...
0
votes
2answers
218 views

$f(x) = f(x-1)*b \to f(x) = c_1 b^{x-1}$

I'm trying to teach myself mathematics. I only started last year with a previous knowledge of basic arithmetic. I often make a detour into regions featuring problems that are a bit too deep for me. ...