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2. Given: A and B are two matrices of order 2x2. Prove that the sum of the entries of the main diagonal of AB-BA is zero.

3. A, B and C are three matrices of order 2x2. Given: A^2 is a scalar matrix and the sum of the entries of the main diagonal of AB-BA is zero. Prove that C (AB-BA) ^2= (AB-BA) ^2*C?