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adartsesirhc
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Homework Statement
Prove the following theorem:
A(BC)=(AB)C.
Homework Equations
http://en.wikipedia.org/wiki/Matrix_multiplication#Ordinary_matrix_product"
The Attempt at a Solution
Let A be of order m by n, B be of order n by p, and C be of order p by q. Then
[tex](A(BC))_{ij}=\sum^{n}_{k=1} A_{ik}(BC)_{kj}=\sum^{n}_{k=1} (A_{ik}(\sum^{p}_{r=1} B_{kr}C_{rj}))[/tex]
After this, I'm stuck. How do I put the summations together, and how should I change the indices of summation?
Thanks!
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