Stitz-Zeager_College_Algebra_e-book

# B if rp rotates a point counterclockwise 45 what

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Unformatted text preview: , A + B = [aij ]m×n + [bij ]m×n = [aij + bij ]m×n = [bij + aij ]m×n = [bij ]m×n + [aij ]m×n = B + A where the second equality is the deﬁnition of A + B , the third equality holds by the commutative law of real number addition, and the fourth equality is the deﬁnition of B + A. In other words, matrix addition is commutative because real number addition is. A similar argument shows the associative law of matrix addition also holds, inherited in turn from the associative law of real number addition. Speciﬁcally, for matrices A, B , and C of the same size, (A + B )+ C = A +(B + C ). In other words, when adding more than two matrices, it doesn’t matter how they are grouped. This means that we can write A + B + C without parentheses and there is no ambiguity as to what this means.3 These properties and more are summarized in the following theorem. Theorem 8.3. Properties of Matrix Addition • Commutative Property: For all m × n matrices, A + B = B + A • Associative Property: For all m × n matrices, (A...
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