# Tagged Questions

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

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### Free-fall air resistance problem

I´m working on a free fall problem and I got an equation with variable $k$ when the situation has air resistance. Then I compared with no air resistance equation ($-4.9$, considering t variable). So, ...
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### FindInstance only satisfies half of my double inequality

FindInstance[ 298973528525.436 < 10^10*(n - k*3.32192809488736) < 298973528539.862, {n, k}, Integers ] Result is: ...
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### How to select one solution of a system? [duplicate]

The system, Solve[{F[x,y]==0,G[x,y]==0},{x,y}] has to solutions {{x->x0,y->y0}} How can I choose, for example, <...
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### how to find sum of variable c1+c2+c3 for expression combinations

how to find sum of variable c1 + c2 + c3 for expression combinations: ...
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### Solving wave PDE

I am trying to solve the wave PDE with NDSolve. Below is the equation: ...
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### Solve does not seem to work for this equation

I need to solve the following equation, for which I am using Solve as below ...
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### How to Count the number of roots in the Domain from an equation

How do i Count[] the number of roots in the Domain and printout the intervals in x containing these roots. Given the function <...
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### Why timing of FindRoot is almost the same even if the function is speedup significantly

This question is almost the same issue as this one. However, it seems that it didn't draw enough attention. Now I encountered the same problem. I previously make this post, I will copy the code here. ...
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### Solving pure functions

I've been trying to use Solve with pure functions to receive function efinition and then use it with Map , to obtain results from mapping function to some data. Here is example ...
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### best way for finding approximate root of monotonic sawtooth like function

First I will generate such kind of monotonic sawtooth like function called func ...
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### How can I set a solution of NSolve into the variable [duplicate]

I am trying to solve an equation such as: NSolve[Integrate[G[x], {x, -∞, ∞}] == 1 && B > 0, B] when ...
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### Reduce function with simultaneous equations and inequalities

I have some simultaneous equations that I want to solve, preferably analytically, yet I am unsure if the Reduce function is the correct route as it doesn't seem to ...
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### Impose a boundary condition to a function

Background I am trying to impose a boundary condition on a function of two variables $u(x_1,x_2)$. The boundary condition is: $u(x_1,0)=A\cos(\omega x_1)$. The same function in mathematica $u(x_1,0)$...
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### Equation for the line of intersection between two planes

I have two equations: 2x + y + z = 1 3x - 2y - z = 5 And I have calculated the answers on paper, which gave me $x = 1 + t$, $y = -1 + 5t$ and $z = -7t$. So my ...
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### Solvability of a system of equations and inequalities

I want to know if a given system of equalities and inequalities is solvable or not. I do not need the solution, rather just about its solvability. I tried a few variations, but I believe that it can ...
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### Finding roots of a function that includes Bessel functions [duplicate]

I'm fairly new to Mathematica so forgive any stupid mistakes. Here's my function: ...
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### Select positive solution based on value of parameter

I want to select positive solutions to Solve[], but as the sign of the solutions depend on the value of some parameters/other variable, I am not sure how to do this?...
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### Differential equation [closed]

How does one solve this differential equation? $$y' = \frac{x^3 + 2x^2 y - y^3}{x^3 + x^2 y}$$
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### Solve homogeneous system [closed]

Let x^2*y + x^2*z + x*y^2 + y^2*z + xz^2 + yz^2+ xyz =0 x^3-xyz + x^2*y-xyz + x^2*z-xyz + xy^2-xyz - xy*z+y^2*z - xyz+xz^2 - xyz+yz^2 =0 x^3+3*xyz+7*yz^2 + xy*z+y^3+9*y*z^2 + x^2*y+6*xyz+4*y*z^2 ...