Hello Seungpyo Kang,
I observe that you want to solve a fourth-degree equation (quartic equation) in a similar manner in MATLAB, so, you will utilize the Symbolic Math Toolbox just like you did for the quadratic equation. A fourth-degree equation has the general form: 
Here is how you can solve it using MATLAB's symbolic capabilities:
syms a b c d e x
eqn = a*x^4 + b*x^3 + c*x^2 + d*x + e == 0;
solx = solve(eqn, x)
Since it is a fourth-degree equation, you can expect up to four solutions (including complex solutions).
To present a specific example using the equation 
:
:syms x
eqn = 2*x^4 - 3*x^3 + x^2 - 5*x + 2 == 0;
solx = solve(eqn, x);
% Approximate solutions to 15 decimal places
solx_numeric = vpa(solx, 15);
% Display numerical solutions
disp(solx_numeric)
To get explicit numerical values of the solutions, you can use the vpa function (Variable Precision Arithmetic) to approximate the roots to a desired number (here, 15) of decimal places.
I hope this answer helps you with your problem.
