True / False Questions If true, explain. Iffalse, give a 2 ( 2 counterexample. (a) A diagonal

Question:

True / False Questions If true, explain. Iffalse, give a 2 ( 2 counterexample.
(a) A diagonal matrix is invertible if and only if its diagonal elements are nonzero. True or false?
(b) An upper triangular matrix is invertible if and only if its diagonal elements are nonzero. True or false?
(c) If A and B are n ( n matrices such that A is invertible, then ABA-1 = B. True or false?