# Solving Inequalities with Matlab

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Dimitrios Anagnostou on 27 Mar 2023
Commented: Walter Roberson on 27 Mar 2023
I guess this is a frequent question here but the answers I have seen did not help me.
I want to solve the following inequality: |x-2| > 2|x+1|.
Manually, we get
In Mathematica there is the built-in function Reduce.
In[58]:= Reduce[Abs[x - 2] > 2 Abs[x + 1], x, Reals]
Out[58]= -4 < x < 0
With Matlab I get
>> version
ans =
'9.13.0.2105380 (R2022b) Update 2'
>> syms x real
>> solve(abs(x-2) > 2*abs(x+1), x)
ans =
-2
There is this answer here that uses Mupad's Solve function but apparently it does not work anymore.
Is there a way to use a Matlab function, not necessarily solve to get the correct domain? Thank you very much.

Dyuman Joshi on 27 Mar 2023
You need to use 'ReturnConditions' as true to obtain the conditions on the solution
syms x real
sol=solve(abs(x-2) > 2*abs(x+1), x,'ReturnConditions',true)
sol = struct with fields:
x: x parameters: x conditions: x < 0 & -4 < x
Steven Lord on 27 Mar 2023
Yes, on the documentation page for the solve function. This documentation page also includes an example, "Solve Inequalities", that shows its use.
Walter Roberson on 27 Mar 2023

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