Question

Which of the following is NOT correct? (A, B and C are matrices)

(a) A.B = B.A

(b) A.B.C = (A.B).C = A.(B.C)

(c) C(A+B) = C.A + C.B

(d) 1 A = A 1

I have been asked this question in examination.

The doubt is from Composite 2D Transformations topic in portion 2D Transformation and Viewing of Computer Graphics

Answer 1

Correct choice is (a) A.B = B.A

The best explanation: Matrix multiplication does not commute. We cannot switch the order of the factors and expect to end up with the same result. Hence, A.B ≠ B.A.