solve 4 equations with 4 unknows

function polynomial()
%Write the equations
syms a 
syms b 
syms c 
syms d
equation1=(a*xk6+b*xk5+c*xk4+d*xk3-xk3yk);
equation2=(a*xk5+b*xk4+c*xk3+d*xk2-xk2yk);
equation3=(a*xk4+b*xk3+c*xk2+d*xk-xkyk);
equation4=(a*xk3+b*xk2+c*xk+d*n-yk);
sol.a=solve(equation1,equation2,equation3,equation4);            UNKNOWNS a,b,c,d . others knowns.
P3=a*x^3+b*x^2+c*x+d;
disp('P3(x)=');
disp(P3);
end

That solution gives me ;

P3(x)=
a*x^3 + b*x^2 + c*x + d
ans = 
    a: [1x1 sym]
    b: [1x1 sym]
    c: [1x1 sym]
    d: [1x1 sym]

BUT I WANT REAL NUMBERS NOT MATRIX. PLEASE HELP IMMEDIATELY.

[Walter Roberson]

You have several undefined variables there, such as xk6.

You sent me email with a variation of this code in which some of those variables were calculated based upon input(), but you did not include sample inputs to test with.

You are passing multiple equations into solve(). You will either get back the empty array or a structure of values. You assign the structure to sol.a but you never use the structure afterwards: you proceed to use a, b, c, d that are still the "syms" that you calculated before. You should

subs(P3, sol.a)

[Rik]

This time I edited your question for you. Next time, please use the tools explained on this page to make your question more readable.