For questions related to usage of Wolfram Alpha.

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2
votes
1answer
63 views

Wolfram-Alpha's choice of $k$ in a complex logarithm

I'm puzzling on this complex integral: $$ \int \frac{2ie^{it}}{2e^{it} - 1}dt = \log(2e^{it} -1)$$ The numerator is the derivative of the divisor, so the primitive is the log of the divisor. When ...
2
votes
2answers
124 views

WolframAlpha seems to suggest that $log(z) = log(-z)$

Wolfram-Alpha returns this snippet at the end of the "step by step solution": I'm confused by the negation of the expression inside the logarithm. The definition of complex logarithm is: $$log(z) ...
0
votes
1answer
1k views

Matrix math syntax in wolfram alpha

I'm having trouble getting Wolfram Alpha to do my bidding with regard to matrix manipulations. I am trying to take the derivative of the following matrix expression with respect to ...
1
vote
2answers
129 views

What is this question asking me? Help appreciated!

I was wondering if anyone would be able to help me understand what this question is asking me. How would I go about working these out on Wolfram Alpha? I'm not too sure how to input them. Any help is ...
2
votes
1answer
96 views

Is WolframAlpha computing this radical correctly?

Is WolframAlpha computing this radical correctly? $$\sqrt{\frac{1}{1 + {10}^{-375}}}$$ When I double-check again, the inequality: $$\sqrt{\frac{1}{1 + {10}^{-x}}} > 1$$ leads to a ...
0
votes
1answer
1k views

Label x axis in radians WolframAlpha

I am trying to graph a trig function in WolframAlpha. I want the x axis to show radians. It will do this for a basic function, such as $y=\sin x$, but for many functions it will just label the x axis ...
1
vote
2answers
336 views

Falling/Rising factorials on WolframAlpha

Is there any notation to input falling or rising factorials on WolframAlpha?, the site has info about but i cant find nothing more.
0
votes
1answer
407 views

How to solve this linear set of equations using W|A?

I try to solve a simple system of four linear equations in the variables ch1, ch2, co1 and co2: ...
3
votes
1answer
177 views

What's wrong with Wolfram Alpha (or me)? Integral involving exp(-t)

The integral in question $\int e^{-t}\cdot (1+e^{-t})^{-2}dt$ can be solved with an easy $u$-substitution. I'm getting $(1+e^{-t})^{-1}$ which I can verify is correct by derivation. I'm rusty though ...
3
votes
2answers
126 views

Wolfram double solution to $\int{x \cdot \sin^2(x) dx}$

I calculated this integral : $$\int{x \cdot \sin^2(x) dx}$$ By parts, knowing that $\int{\sin^2(x) dx} = \frac{1}{2} \cdot x - \frac{1}{4} \cdot \sin(2x) +c$. So I can consider $\sin^2(x)$ a ...
-3
votes
4answers
320 views

Why does Wolfram Alpha say that $\sqrt{1}=-1$? [duplicate]

Why does Wolfram Alpha say that $\sqrt{1}=-1$? Is this a mistake or what? Can anyone help? Thanks in advance.
2
votes
1answer
578 views

Input integral derivative in Wolfram Alpha

How to input $\frac{d}{dx}(\int_0^x \sqrt{t^2-t+1} \,dt)$ in Wolfram Alpha? If i change $dt$ by $dx$ it works, but the output is $\sqrt{t^2-t+1}$, there is no substitution for "$t$" there, if i am ...
0
votes
1answer
416 views

Input expression with summations in Wolfram Alpha

Wolfram understand this expression , but i need to do the limit when n tends to infinity of that expression . As you can see in the wolfram web itself, in the last link it fails to understand the ...
0
votes
1answer
210 views

Large system of equations using wolfram alpha.

I'm trying to use Wolfram Alpha to solve a very large system of equations- Variables A through P with a Z. It has 40 equations, so it won't let me use the regular type in the first bar. I tried using ...
2
votes
1answer
837 views

How to compute the modular multiplicative inverse on WolframAlpha?

$e = 17$ $\varphi(3233) = (61 - 1)(53 - 1) = 3120$ Compute d, the modular multiplicative inverse of e (mod φ(n)) yielding d = 2753. ...
1
vote
2answers
125 views

derivative, the way to show in a graph

http://www.wolframalpha.com/input/?i=derivative+x%5E2%2C+x%5E2 Just reminding myself some math.. Is it ok to show the derivative in such a way like was shown in the link above for $x^2$ function? A ...
1
vote
1answer
99 views

Nonlinear regression analysis of a vector

I'm trying to get a nonlinear fit of a vector in Matlab with no success. Let's assume that I have a vector called data: data = [1,30,250,55,22,76] which can be ...
2
votes
1answer
2k views

How to input this into Wolfram Alpha?

I wish to simplify a sum by doing "simplify sum_{a=0}^L f(a)" where $f(a)$ is just some arbitrary expression, but I want to only do the sum when some condition is met. Using the Iverson brackets, I ...
1
vote
1answer
56 views

Using Wolfram to convert a value chart into graph

Is it possible to use Wolfram Alpha to make something like this into a graph and have it display the proper function? In that case, how would I syntactically write it in Wolfram?
1
vote
1answer
1k views

How do I input these interval equation in to wolfram to show me the solution

How do I enter these equation into wolfram to show me the interval type equation which gives the solution as exact values.. Question 1 : $2\tan x\cos x = \tan x$ where $0\leq x< 2\pi$ Question 2: ...
0
votes
2answers
135 views

How do I enter the equation $y=\sin\frac{2\pi }{3}x$ into Wolfram Alpha? [closed]

How do I enter this equation into wolfram? Any help would be much appreciated. I'm not sure how to do the brackets. $$y=\sin\frac{2\pi }{3}x$$
2
votes
3answers
260 views

arithmetic operations on alephs in WolframAlpha

Can someone please enlighten me if or how both of these facts can be true? I entered $\aleph_0-\aleph_0$ into WolframAlpha, which gave the result as undefined. But it also plotted the result on a ...
1
vote
1answer
114 views

Am I right or is Wolfram right?

Let ${a_n}$ be a sequence whose corresponding power series $A(x)=\sum_{i\geq 0}a_ix^i$ satisfies $$A(x)=\frac{6-x+5x^2}{1-3x^2-2x^3}$$ Determine a recurrence relation that ${a_n}$ satisfies. I ...
4
votes
1answer
77 views

Polar coordinations - problem with r and $\theta$

let's take a look on Archimedean spiral. the polar equation is $r = \theta$. click here to look. but $\tan (\theta) = y/x$ and $r = \sqrt{x^2+y^2}$, so $r = \theta \rightarrow \tan(\sqrt{x^2+y^2}) ...
0
votes
2answers
129 views

Series expansion with remaining $log n$

I'm studying the asymptotic behavior $(n \rightarrow \infty)$ of the following formula, where $k$ is a given constant. $$ \frac{1}{n^{k(k+1)/(2n)}(2kn−k(1+k) \ln n)^2}$$ I'm trying to do a series ...
0
votes
1answer
798 views

Mathematica vs Wolfram Alpha integration results

When I insert the following integration command in wolframalpha: ...
1
vote
0answers
93 views

Strange results for solving boundary angle of full reflection

I was trying to solve the following group of equations for $\alpha$ using Wolfram|Alpha: $$\frac{v_2\cdot\sin(\alpha)}{v_1} = 1 \\ v_1 > 0 \\ v_2 > 0$$ I expected something like $\alpha = ...
5
votes
1answer
188 views

Why doesn't $ \lim_{(x,y)\rightarrow(0,0)} xy\sin(\frac{1}{xy}) $ exist?

I've tried to get the following limit: $$ \lim_{(x,y)\rightarrow(0,0)} xy\sin\left(\frac{1}{xy}\right) $$ wolfram claims it doesn't exist. How to show that? Why can't I take $z=xy$ and receive a ...
1
vote
1answer
389 views

Numerical values of the Jacobi elliptic function sn: Wolfram Alpha vs. Maple vs. C++?

I have a problem to check the validity of an algorithm I've implemented in C++ to compute the Jacobi elliptic function $\mathrm{sn}(u, k)$ (inspired and improved from Numerical Recipes 3rd edition). I ...
0
votes
1answer
233 views

Is Wolfram Alpha correct?

Given the attempted derivative at http://www.wolframalpha.com/input/?i=d%28a%28x%29+choose+b%28x%29%29%2Fdx, I believe the result from Wolfram Alpha is off by a factor of 2 or, at least I get a result ...
0
votes
2answers
691 views

How to solve this graph problem in WolframAlpha?

I need to input this problem in WolframAlpha: Write an equation of the line containing the given point and parallel to the given line: $(8,-8)$, $7x+8y=5$. The answer is $7x+8y=-8$ but I'm not ...
0
votes
1answer
779 views

What does a dot after a number mean?

So I'm making some calculations for numerical analysis and the output I get in Wolfram or Mathematica for input like: ...
13
votes
4answers
636 views

The last few digits of $0^0$ are $\ldots0000000001$ (according to WolframAlpha).

Can anybody explain how this comes about?
2
votes
4answers
2k views

Wolframalpha - how to get value of function in a specific point?

For example , given this function - $f(x) = x^3-x^2-x-1$ and I want to check it in the point $x=1.6$. What should I have to write in the command line of wolframalpha in order to get it ?
1
vote
3answers
123 views

Generating function with quadratic coefficients.

$h_k=2k^2+2k+1$. I need the generating function $$G(x)=h_0+h_1x+\dots+h_kx^k+\dots$$ I do not have to simplify this, yet I'd really like to know how Wolfram computed this sum as ...
0
votes
1answer
686 views

How to calculate vector * matrix-inversed in Wolfram Alpha?

I am trying to calculate the product of a vector and an inversed matrix in wolfram alpha: $\begin{bmatrix}1 & 2 & 3\end{bmatrix}$ * $\begin{bmatrix} -0.5 & 0 & 0 \\ 3 & 1 & 0 ...
0
votes
1answer
442 views

Getting weird integral evaluation from Wolfram Alpha

Check this out. I hand-evaluated this integral and my pretty sure the answer is zero, but Wolfram returns the value $4i\pi$ instead.
0
votes
1answer
61 views

Permutations - bug in Wolfram Alpha?

I've got question whether Wolfram Alpha has bug in showing permutations. Check permutation rules, list, and two-line notation in this permutation. I'd expect same result as was on Wolfram Alpha blog ...
1
vote
2answers
663 views

Wolframalpha step-by-step of $\int\frac{\cos(x)}{\sqrt{2+\cos(2x)}}dx$

I wonder, where the minus sign goes after the first $u$-substitution of integral $\displaystyle\int\frac{\cos(x)}{\sqrt{2+\cos(2x)}}dx$?
6
votes
4answers
562 views

Why WolframAlpha Result is Different?

http://www.wolframalpha.com/input/?i=x%3D10%5E-15%3B+%28e%5Ex-1%29%2Fx When i click Approximate Form in result, the result is: ...
4
votes
5answers
990 views

Find the second derivative of $e^{x^{3}}+7x$

$$e^{x^{3}}+7x$$ Here is what I have tried so far, $$y'=(e^{x^{3}})'+(7x)'$$ $$y'=3e^{x^{2}}e^x+7$$ $$y'=3e^{x^{3}+x}+7$$ I am supposed to find the second derivative but I believe I have already made ...
0
votes
1answer
194 views

Equation with 2 variables tricky problem

So let's say I have some random equation $6yx^3 - 3yx + 5 = 0$, but could be anything. How would I go about finding a value for $y$, that makes it so that this equation only holds true if $x$ is ...
17
votes
4answers
1k views

Wrong Wolfram|Alpha limit?

I have this function: $$ f(x,y) = \frac {xy}{|x|+|y|} $$ And I want to evaluate it's limit when $$ (x,y) \to (0,0)$$ My guess is that it tends to zero. So, by definition, if: $$ \forall \varepsilon ...
7
votes
3answers
2k 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
11k 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
483 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
1k 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
39 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
973 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
160 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 ...