Solution of symbolic fourth order polynomial equation

I am finding difficulty in finding roots of a fourth order polynomial equation which as as follows:

lambda^4+A*lambda^2-B*lambda+C=0

where A, B, and C are constants. I used function roots() function in matlab, but it doesnt worked.

Answer 1

[VBBV]

A = 2;
B = 1.4;
C = 3

C = 3

syms L
eqn = L^4 + A*L^2 - B*L + C == 0

eqn = 

sol = double(vpasolve(eqn,2))

sol = 
  -0.6390 + 1.3986i
  -0.6390 - 1.3986i
   0.6390 + 0.9277i
   0.6390 - 0.9277i

Try using vpasolve

Answer 2

[hiluf]

a=-32;
b=4;
c=-8;
d=4;
syms L
egn=L*exp(4)+L*exp(2)+L*c+d==0;
sol = double(vpasolve(eqn,2));

Answer 3

[Walter Roberson]

You can get the complete symbolic solution... or a placeholder form that in practice is much more convenient.

syms lambda A B C
eqn = lambda^4+A*lambda^2-B*lambda+C == 0

eqn = 

sol_root = solve(eqn)

sol_root = 

sol_full = solve(eqn, 'maxdegree', 4)

sol_full =