Solve an equation of fourth degree with two variables

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]

what error you got?

[AAA]

Error using mupadmex

Error in MuPAD command: Index exceeds matrix dimensions.

Error in sym/subsref (line 1577)

        B = mupadmex('symobj::subsref',A.s,inds{:});

Error in Hw4 (line 7)

x1_sol(9);

[Walter Roberson]

*/ is not a valid operation.

Answer 1

[Valmir Sadiku]

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!

[AAA]

I'm trying to set the parameter value Y to calculate X.

I want to calculate the value of X for a vector of Y. How do I do this?

[Valmir Sadiku]

as far i understand you will solve this equation system:

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);
y = 9;

if there so, you can do it in this way:

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, y ==9);

hopefully it will help you!

[Walter Roberson]

Yvals = linspace(-10, 10, 101);
Xvals = double(subs(x_sol, y, Yvals));

[Valmir Sadiku]

i never saw this command 'subs' bevor, so i think now you got the solution of your problem?

[AAA]

yes, it's exactly what I needed. thanks!