Matrices X and Y both measure 2 times 2 and are inverses of each other. Which matrix represents their product?

A matrix multiplied by its inverse gives the identity matrix: XY = I (and also YX = I). For a 2 by 2 matrix, the identity matrix has 1s on the main diagonal and 0s elsewhere, so it is the matrix with rows (1, 0) and (0, 1). That is choice D.

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