Math: matrices
posted by mathstudent .
If A and B are both square n x n matrices,
If AB = I,
prove BA = I
Presumably you have to do this without using the usual properties of the inverse of matrices. But we do need to use that if there exists a matrix B such that
A B = I
then the equation A X = 0 has the unique solution:
X = 0
So, let's start with:
AB = I
Multiply both sides by A on the right:
(AB)A = A
Now you use that (AB)A = A(BA) and you can rewrite the above equation as:
A(BA  I) = 0
And it follows that
BA = I
well if u decmial the 7 to a 6 good luck with that ..........
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