If A and B are two invertible square matrices of same order, then what is (AB)^$$-$$1 equal to?

Consider the following in respect of matrices A, B and C of same order.

1. (A + B + C)' = A' + B' + C'

2. (AB)' = A' B'

3. (ABC)' = C' B' A'

Where, A' is the transpose of the matrix A. Which of the above are correct?

Consider the following in respect of matrices A and B of same order.

1. A² $$-$$ B² = (A + B) (A $$-$$ B)

2. (A $$-$$ I) (I + A) = O $$ \Leftrightarrow $$ A² = I

where, I is the identity matrix and O is the null matrix.

Which of the above is/are correct?

What is the adjoint of the matrix $$\left( {\matrix{ {\cos ( - \theta )} & { - \sin ( - \theta )} \cr { - \sin ( - \theta )} & {\cos ( - \theta )} \cr } } \right)$$ ?