# Solve an equation of fourth degree with two variables

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AAA on 22 May 2013
I have to solve an equation of fourth degree with two variables, and draw the line where it is equal to zero. I tried to do that but I got an error message when I tried to place a value in x1_sol:
syms x y;
v=1/16*(3*x+17*y/3)*(-x^3-6*y^2-11*x+y)+1/96*(34*x+130*y)*/(3*x-y);
x_sol=solve(v==0,x,'MaxDegree', 4);
x1_sol=x_sol(1);
x1_sol(9);
Where am I wrong? Do I use the right way?

Valmir Sadiku on 22 May 2013
what error you got?
AAA on 23 May 2013
Error in MuPAD command: Index exceeds matrix dimensions.
Error in sym/subsref (line 1577)
Error in Hw4 (line 7)
x1_sol(9);
Walter Roberson on 23 May 2013
*/ is not a valid operation.

Valmir Sadiku on 23 May 2013
i don't know what you are trying with this command x1_sol=x_sol(1); because the size of the x_sol are:
>> size(x_sol)
ans =
1 1
that's because it should be clear why x1_sol(9); give you an error message!

Walter Roberson on 23 May 2013
Yvals = linspace(-10, 10, 101);
Xvals = double(subs(x_sol, y, Yvals));
Valmir Sadiku on 23 May 2013
i never saw this command 'subs' bevor, so i think now you got the solution of your problem?
AAA on 24 May 2013
yes, it's exactly what I needed. thanks!