# Questions tagged [equation-solving]

Questions on the analytic and numerical equation solving functions of Mathematica (Solve, Reduce, NSolve, FindRoot, DSolve, RSolve, etc.).

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### Command to know when it become constant

So I got this equations and I want to know if there is a command to know when the function becomes constant and obtain that value, this is my code and I know that approximately at 2600 both functions ...
1answer
62 views

### Reduce the time to find six integer numbers so that the angle of two vectors equal to Pi/6

I am trying to find six integer numbers a, b, c, x, y, z so that the angle of two vector {a, b, c and ...
1answer
101 views

### How is Mathematica treating $x^x$ when finding roots?

When I enter Solve[x (-x + x^x) == 0, {x}, Reals] It returns three roots as $$\{\{x\to -1\},\{x\to 1\},\{x\to 1\}\}$$ Is MMA treating ...
1answer
38 views

This hangs: ...
0answers
24 views

### Why doesn't work the maximize and reduce?

Alguien puede ayudarme por favor? He estado tratando de resolver y hallar en base a las funciones maximizar y reducir, la expresion de P y sus restricciones, pero no he podido obtener. ...
1answer
47 views

### How can I use “Reduce” to solve equation with complicated form?

Here I used Reduce to solve that complicated equation in complexes but MMA didn't give an answer after a few mins. I wonder whether there're some functions could ...
0answers
31 views

### Rescale root of quartic equation

I have a quartic equation $1-r+\frac{1}{w^2}r^4=0$ where I am interested in the plot of $\frac{1}{w} f(r_0)$ (equal to $f(r_0/w)$) where $r_0$ is one of the roots. I would like to rescale the roots ...
0answers
30 views

### Assume some expression is false

I need to Reduce a complicated function and I want to exclude some conditions A and B. How do I assume that the expression A is ...
1answer
62 views

### How to get the intersection between circle and rectangle?

Consider two figures: a rectangle with coordinates $(x_{min},y_{min}), (x_{min}+dx,y_{min}+dy)$, and a circle. The latter has a radius $R$ and is located at the center of the coordinate frame. How to ...
2answers
98 views

2answers
71 views

### Solving a recursive equation iteratively (including PolyLog function)

I have the following equation which I want to solve: $$I_D = [Li_2(-e^{V_D-I_D})-Li_{2}(e^{I_D})]$$ Here $Li_2(x)$ is the PolyLog function of order $2$. Is there a way to solve this equation ...
1answer
55 views

### Finding the joint domain for a couple of functions of three variables

I have two functions $f_{1}(x,y,z)$ and $f_{2}(x,y,z)$ defined respectively as ...
1answer
23 views

### Manipulate parametters inside NSolve with complex variable

I think my question should be simple but I couldn't figure out a nice way to do it. I want to find zeros of a complex function (variable $z$) with real parameters ($\nu$, $\alpha$, $\xi$). My goal is ...
1answer
59 views

### FindRoot not obtaining solution for nonlinear system of log equations

There is a system of 9 non-linear equations, eq containing logarithms that I think it should be solvable numerically. There are a total of 9 variables with two of ...
1answer
46 views

### How to refer a solve answer to NDsolve [closed]

I don't know how to refer a solution of Solve to compute it in NDSolve, here's my code ...
1answer
30 views

### Read the graphic at another value

So I got this code and I'm new at coding, what I want to do is just read the graphic at a value of the Y axis and get the value of the X axis ...
2answers
59 views

### Obtaining the other axis value

I'm new at coding and I got this simple differential equiation and the plot of this function involved, I can obtain the value of the dependant variable based on the independant varible as usual, what ...
1answer
231 views

### How to solve vector equation?

Given the vector relation $(\mathbf{a}+3 \mathbf{b}) \perp(7 \mathbf{a}-5 \mathbf{b})$, $(\mathbf{a}-4 \mathbf{b}) \perp(7 \mathbf{a}-2 \mathbf{b})$, find the angle between $\mathbf{a}$ and \$\mathbf{b}...