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