Jika [tex]\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) [/tex],nila

[tex] \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}\frac{1}{a-b}&\frac{b}{a-b}\\0&1\end{array}\right] = \left[\begin{array}{ccc}a&1\\-a+2b&1\end{array}\right] [/tex]

*
0 = -a + 2b
-2b = -a
a = 2b

*
1/(a-b) = a
1/(2b-b) = 2b
1/b = 2b
1 = 2b.b
1 = 2b²
b² = 1/2
b = √1/2

*
0 = -a + 2b
0 = -a + 2√1/2
-2√1/2 = -a
a = 2√1/2

*
ab
= 2√1/2 . √1/2
= 2. 1/2
= 1