Solution of symbolic fourth order polynomial equation

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Susmita Panda
Susmita Panda 2021-11-13
回答： Walter Roberson 2023-10-19
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.

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采纳的回答

VBBV
VBBV 2021-11-13
编辑：VBBV 2021-11-13
Ran in:
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

更多回答（2 个）

hiluf
hiluf 2023-10-19
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));
Walter Roberson
Walter Roberson 2023-10-19
Ran in:
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 = 

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