0. An arbitary vector X is an eigen vector of the matrix
then (a,b)=
(X1,X2,X3) is an arbitary eigen vector, say corresponding to 1, then
X2 X3 being not zero, we have
X1 = X1 ; aX2 = X2
which gives a = 1
and bX3 = X3
which gives b - 1
(a, b) = (1, 1)