Solving system of 3 non-linear equations.

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Hello, I'm trying to solve a system of equations using matlab.
The three variables are: xo2, xo, xar
I've entered the equations in as follows:
syms xo2 xo xar
eq1 = xo2 +xo +xar = 1
eq2 = 2*xo2 +xo -4*xar = 0
eq3 = 2.063E-4*xo2 = xo^2
Then, to solve the system for the variable xo I typed:
solve('eq1', 'eq2', 'eq3', xo)
and I get this message: Warning: Explicit solution could not be found.
What am I doing wrong? I'm fairly ceratain that this system is solvable.
is it because I am using symbolic algebra? For hte problem that I am solving, I dont need a general expression for the value, I just need a number.

Accepted Answer

Oleg Komarov
Oleg Komarov on 13 Feb 2011
Rewrite as:
syms xo2 xo xar
eq1 = xo2 +xo +xar - 1;
eq2 = 2*xo2 +xo -4*xar;
eq3 = 2.063E-4*xo2 - xo^2;
sol = solve(eq1,eq2,eq3);
sol.xo
Oleg
  3 Comments
Adithya Valavi
Adithya Valavi on 24 Mar 2020
Plz tell me if you knew how to solve this equations
Christopher Creutzig
Christopher Creutzig on 25 Mar 2020
Adithya Valavi, did you try vpasolve?
It's usually a good idea to post a new problem in a new question, rather than adding a comment to something related.

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More Answers (4)

Pierce Brady
Pierce Brady on 30 Mar 2011
the output class will be syms, so try casting the answer to a double
class(ans)
double(ans)
class(ans)

Pier Giorgio Petrolini
Pier Giorgio Petrolini on 23 Mar 2020
I hope it can be already helpfull...
syms x y z
eq1=exp(x)+sqrt(y)-z.^3-2
eq2=x.^2-y-z-5
eq3=x+exp(y-1)+z-7
eqs = [eq1, eq2, eq3]
[x,y,z]=vpasolve(eqs,[x,y,z])
% Reported results
x = -2.8;
y = 3.33;
z = -0.48;
  1 Comment
Stephen Ofori
Stephen Ofori on 13 Jan 2023
This is also working, but the approximations makes it unsuitable for solutions where very small errors are required. If your work require minimal error then it is better to use the solve or fsolve.

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Tushar
Tushar on 13 Feb 2011
Ah thanks, excellent.
Now the only problem is that when I use your code, matlab spits out a crazy number like this:
ans =
- 2995371679198674497313343284804110513^(1/2)/147573952589676412928 - 12685211008020935/147573952589676412928
how do I get it to something more readable.. like scientific notation or something
  2 Comments
Walter Roberson
Walter Roberson on 14 Feb 2011
Use vpa() or double() to get the number in decimal format.

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YARA NABA
YARA NABA on 10 Mar 2019
syms x y z
eq1=exp(x)+sqrt(y)-z.^3-2
eq2=x.^2-y-z-5
eq3=x+exp(y-1)+z-7
sol=solve(eq1,eq2,eq3)
sol
how can i rewrite it

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