0. The eigen vectors of a real symmetric matrix corresponding to different eigen values are
AT=A
Let α1 and α2 be different eigen values of matrix A, and X1 and X2 be the corresponding vectors, then
AX1= α1X1 and AX2 = α2X2
Taking transpose of the second equation
(AX2)T= (α2X2)
X2TAT= α2.X2T 2X2T
But AT-A
Post multiply by X1, we get
XT2AX1 = a2 X2T X1
But AX1 = a1X1
XT2 a1X1 = a2 X2T X1
(a1 - a2) X2TX1 = 0
Since a1
a2, a1 - a2 0X2TX1 = 0 i.e. X2 and X1 are orthogonal.