Tuesday, 10 February 2015

linear algebra - Showing that a Matrix is Nonsingular



Let n be a positive integer and let F be a field. Let AMn×n(F) be a matrix for which there exists a matrix BMn×n(F) satisfying I+A+AB=O. Show that A is nonsingular.




Since I+A+AB=O, we can get
I+A(I+B)=0
A[(I+B)]=I



I know it seems (I+B) is the inverse of A, however, I am not sure how to get
(I+B)A=I. I may choose a wrong way to solve this problem. I am really stuck with this question.


Answer



In+A+AB=OIn+A(In+B)=OA(In+B)=In. Take determinant of both sides gives det(A)det(In+B)=(1)n, hence det(A) is non-zero and A is invertible.


No comments:

Post a Comment

real analysis - How to find limhrightarrow0fracsin(ha)h

How to find lim without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...