a) Let A be a 2 × 2 matrix. Show that for ALL choices of scalars a, that if A = aI2, then AB = BA for ALL 2 × 2 matrices B.   b) For ALL 2×2 matrices A where A is NOT a scalar multiple of I2, find a 2 × 2 matrix C with AC ̸= CA (Hint: use matrices with a single nonzero entry.)

Elementary Linear Algebra (MindTap Course List)
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Chapter2: Matrices
Section2.1: Operations With Matrices
Problem 77E
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a) Let A be a 2 × 2 matrix. Show that for ALL choices of scalars a, that if A = aI2, then AB = BA for ALL 2 × 2 matrices B.

 

b) For ALL 2×2 matrices A where A is NOT a scalar multiple of I2, find a 2 × 2 matrix C with AC ̸= CA (Hint: use matrices with a single nonzero entry.)

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