6.
A=[a,1,0; 0,a,1; 1,0,a],
X=[b,c,d; e,f,g; h,i,j]
AX-XA=[ab+e,ac+f,ad+g; ae+h,af+i,ag+j; ah+b,ai+c,aj+d]
-[ab+d,ac+b,ad+c; ae+g,af+e,ag+f; ah+j,ai+h,aj+i]
=[e-d,f-b,g-c; h-g,i-e,j-f; b-j,c-h,d-i]
=[0,0,0; 0,0,0; 0,0,0]
e-d=0, f-b=0, g-c=0, h-g=0, i-e=0, j-f=0, b-j=0, c-h=0, d-i=0
これを解いて
b=f=j=k1,c=g=h=k2,d=e=i=k3 (k1,k2,k3は任意定数)
(答)
X=[k1,k2,k3; k3,k1,k2; k2,k3,k1] (k1,k2,k3は任意定数)