Elementary Linear Algebra 7th Edition

(a) $\langle A, B \rangle =0$ (b) $\| A\| =\sqrt{4}$ (c) $\| B \| =\sqrt{2}$ (d) $d(A,B)=\sqrt{6}.$
$A=\left[\begin{array}{rr}{1} & {0} \\ {0} & {1}\end{array}\right], \quad B=\left[\begin{array}{rr}{0} & {1} \\ {1} & {0}\end{array}\right]$ (a) $\langle A, B \rangle =2a_{11} b_{11}+a_{12} b_{12}+a_{21} b_{21}+2a_{22} b_{22}=0$ (b) $\| A\| =\sqrt{\langle A, A\rangle}=\sqrt{2a_{11}^{2}+a_{12}^{2}+a_{21}^{2}+2a_{22}^{2}}=\sqrt{2+2}=\sqrt{4}$ (c) $\| B \| =\sqrt{\langle B, B\rangle}=\sqrt{2b_{11}^{2}+b_{12}^{2}+b_{21}^{2}+2b_{22}^{2}}=\sqrt{2}$ (d) $d(A,B)=\| A-B \|=\| \left[\begin{array}{rr}{1} & {-1} \\ {-1} & {1}\end{array}\right] \|=\sqrt{2+1+1+2}=\sqrt{6}.$