矩阵B为[3 0 0]
[0 2 0]
[0 0 5/3]
过程很麻烦,就是设出矩阵B为[x1 x2 x3]
[y1 y2 y3]
[z1 z2 z3]
根据AB=A+2B 联立方程得3x1=3+2x1；4y2=4+2y2；5z3=5+2z3；其余为0.