Posted by **LEON** on Sunday, October 24, 2010 at 10:11pm.

How to prove or disprove

(a)if A has a zeronentryonthe diagonal then A is not invertible

(b)if Ais not invertible then for every matrix B, AB is not invertible

(c)if A is a nonzero 2X2 matrix such that A^2+A=0, then A is invertible

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