Question

Suppose matrix D is the inverse of matrix C. Which of the following is equal to D?

O CDD
O CCD
O DDD
O CCC

Answer 1

Answer is First answer choice: CDD

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Step-by-step explanation:

C and D are inverses of each other. When they multiply together, they will produce the identity matrix I

C*D = I

D*C = I

note: this is the uppercase letter 'i' and not the number one. The 'i' stands for 'identity'. Another thing to note is that matrix multiplication is not normally commutative, but it works for matrix inverses.

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So this means C*D*D = (C*D)*D = (I)*D = I*D = D because multiplying the identity matrix with some matrix X leads to the same matrix X.

This is why the first choice is the answer.

The second choice doesn't work because C*C*D = C*(C*D) = C*(I) = C*I = C

The third choice doesn't work because we don't have any C's here. All we can say is that D*D*D = D^3

Similarly choice 4 doesn't work as all we can say is C*C*C = C^3.