Symbolic Toolbox finds no solution to biquadratic equation

Hey all,

I need to solve a very long and komplex and biquadratic equation (ax^4+bx^3+cx^2+dx+e = 0) symbolically, however the symbolic Toolbox does not find a solution. I am aware that there are closed form solutions to biqudratic equations, so it should be possible to find them. Any tipps how i can find these solutions/ make the symbolic tooldbox find them?

I am grateful fo any help.

Yours,

Lukas

Answer 1

[Walter Roberson]

syms A B C D E x
R = solve(A*x^4 + B*x^3 + C*x^2 + D*x^1 + E*x^0, x, 'maxdegree', 4);

now use coeffs on your original expression to extract the expression a matching degree 4, b degree 3, and so on. Then

RR = subs(R, [A, B, C, D, E], [a, b, c, d, e]) ;

These will be long and it is very likely that they will be incomprehensible. If someone were to present the same expressions but with any 3 signs changed you would probably never notice or have any idea what the difference meant physically.

[Lukas Schroth]

Thank you!