%uloha 50
clear
syms a
A=[3 0 a 1;0 a 1 1 ;a 1 1 2;1 1 2 0]
D=det(A)
solve(D) %kdy je matice singularni
Ainv=inv(A)
p=poly(A)

ezplot(subs(p,a,0),[-3,5])
B=subs(A,0)
eig(B)  %eig(subs(A,a,0))