MATLAB: How it is possible to find the eigenvalues of a 2*2 matrice without using of eigen function

eigenvaluematrix

Hi every one,
I tried to fine eigenvalues of 2*2 A matrix with det(A-landa*I) and my script is follow as:
 clc
 clear all
 syms landa
 a=input('please enter value of a:');
 b=input('please enter value of b:');
 c=input('please enter value of c:');
 d=input('please enter value of d:');
 A=[a b; c d];    I=[1 0;0 1];   B=landa*I; 
 D=det(A-B)
firstly, I defined landa as syms and after finding determinant, with a=1, b=2, c=3 and d=4, the result is 'landa^2 – 5*landa – 2' . (it is a 2 degree polynomial that saved in D)
so my problem is: How I could got the coefficients of this polynomial for finding the landa1 and landa2 as eigenvalues of A matrix?

Best Answer

eigenvalues=solve(D==0,landa);
Best wishes
Torsten.
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