Jika \left(\begin{array}{ccc}a-b& &-b\\ & & \\0& &1\end{array}\right) ^{-1} = \left(\begin{array}{ccc}a& &1\\ & & \\-a+2b& &1\end{array}\right) ,nilai ab =

[tex]\displaystyle \left(\begin{array}{ccc}a-b&-b\\0&1\end{array}\right)^{-1} = \left(\begin{array}{ccc}a&1\\-a+2b&1\end{array}\right) \\ \frac{1}{a-b}\left(\begin{array}{ccc}1&b\\0&a-b\end{array}\right)=\left(\begin{array}{ccc}a&1\\-a+2b&1\end{array}\right) \\ \left(\begin{array}{ccc}^1/_{a-b}&^b/_{a-b}\\0&1\end{array}\right)=\left(\begin{array}{ccc}a&1\\-a+2b&1\end{array}\right) \\ -a+2b=0 \\ a=2b \\ \\ ^1/_{a-b}=a \\ 1=a(a-b) \\ 1=2b(2b-b) \\ 2b^2=1 \\ b^2=\frac{1}{2},$ sehingga $b=\pm\frac{1}{\sqrt{2}}[/tex]
Dan,
[tex]a=\pm\frac{1}{\sqrt{2}}\times 2=\pm\sqrt{2} \\ $Maka, ambil yang positif misalkan$ \\ ab=\frac{1}{\sqrt{2}}\times \sqrt{2}=1[/tex]