# Rebelious matrix commutivity

1. Nov 4, 2009

### brandy

hey i was just thinking how matrices aren't supposed to be commutative?
well i was just thinking, what if the matricees were equal? and i was like ha! im so cool! take that mr logic.
so yea, so far i have a couple rebelious matricees
a*b where a=1 by 1 and b= 1 by 1
a*b where na=b
a*b where a^n=b
a*b where a= identity
a*b where na=b and a = identity
a*b where a = null
a*b where a= mutliple of identity and b= multiple of mirrored identity

so, my questiono is this, can you help me be a good little poindexter and come up with a couple others?

Last edited: Nov 4, 2009
2. Nov 4, 2009

### VeeEight

Consider what happens if B = A + xI (for some real number x, I being the identity matrix) and if A and B are diagonal matrices.

3. Nov 4, 2009

### mathman

Both A and B symmetric.