Question

设a为3维列向量,a^T是a的转置,若aa^T=1-11 -11-1 1-11,则a^Ta

Answer 1

简单计算一下即可，答案如图所示

Answer 2

aa^T=
1 -1 1
-1 1 -1
1 -1 1
a^Ta 是矩阵的迹 = 1+1+1 = 3.