Let A and B be invertible matrices such that
A <2 , -1> = <1 , 2> and B <1 , 3> = <2 , -1>.
Calculate (AB)^{-1} <1 , 2>.
\((AB)^{-1}<1,2> =\\ B^{-1}A^{-1}<1,2>\)
\(A<2,-1> = <1,2>\\ <2,-1>=A^{-1}<1,2>\)
\(B<1,3>=<2,-1>\\ <1,3> = B^{-1}<2,-1>\)
\(B^{-1}A^{-1}<1,2> = \\ B^{-1}<2,-1> = \\ <1,3>\)
