Please answer in detail.

TRUE / FALSE with justification

3.22 Let A be a 4 x 3 matrix and B a 3 x 4 matrix. Then AB cannot be invertible. [Hint: Think about rank.]3-26 Suppose that A is an n x n matrix such that AA' = I. Then A'A = I as well. 3-27 Suppose that A is an n x n matrix that satisfies A2 + 7A - I = o. Then A is invertible. 3-28 Suppose that A is invertible and B is row equivalent to A. Then B is invertible. 3-29 Suppose that A is invertible and B is any matrix such that AB is defined. Then AB and B have the same nullspace