Question

证明：设n阶方阵A满足A^2=A,证明A的特征值为1或0

Answer 1

设 a为矩阵A的特征值,X为对应的非零特征向量.
则有 AX = aX.
aX = AX = A^2X = A(AX) = A(aX) = aAX = a(aX) = a^2X,
(a^2 - a)X = 0,
因X为非零向量,所以.
0 = a^2 - a = a(a-1),
a = 0或1.