Prove that if $B$ is an antisymmetric matrix, then $\det(B+I) \neq 0$

201 Views Asked by At

Prove that if $B$ is an antisymmetric matrix with real entries, then $\det(B+I) \neq 0$.

1

There are 1 best solutions below

0
On BEST ANSWER

The matrix $B$ satisfies $B^T=-B$; suppose $\det(B+I)=0$; then there exists $x\ne0$ such that $(B+I)x=0$. It follows that $Bx=-x$ and so $$ x^TBx=-x^Tx $$ Transpose both sides, getting $$ x^TB^Tx=-x^Tx $$ and use the hypothesis $B^T=-B$ to get a contradiction.

(It can be made without contradiction, of course.)