# multiplying matrices

#### matlabnoob

In general ABA is NOT equal to B! And A(ACA)A'= (A^2)C(AA') which is equal to (A^2)C only if AA'= I which is not always true.

thank you both for your help(Wink)
why isnt this always true? if and only if say AA' = I ... it makes sense for it to be true right??

#### dwsmith

MHF Hall of Honor
thank you both for your help(Wink)
why isnt this always true? if and only if say AA' = I ... it makes sense for it to be true right??
If there is no inverse matrix, $$\displaystyle AA^{-1}$$ doesn't exist since $$\displaystyle A^{-1}$$ doesn't exist.