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Warm-Up – October 7. 1). 3). 2). 4.2 Multiplying Matrices. In order to multiply matrices. A • B = AB. m x n. n x p. m x p. Ex 1. These MUST match. Is the product defined? What are the dimensions of AB?. A. B. AB. 2 x 3. 3 x 4. 2 x 4. AB. A. B. 5 x 3. 5 x 2.
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Warm-Up – October 7 1) 3) 2)
In order to multiply matrices... A • B = AB m xn nx p m x p Ex 1. These MUST match Is the product defined? What are the dimensions of AB? A B AB 2 x 3 3 x 4 2 x 4 AB A B 5 x 3 5 x 2 Not defined
How to multiply... Always check dimensions FIRST! ac ad = bd bc 2 x 1 1 x 2 2 x 2
Ex. 1 -2 6 5 -15 2 x 1 1 x 2 2 x 2
How to multiply... ag +bi +ck ah +bj +cm = 2 x 3 3 x 2 2 x 2
How to multiply... ag +bi +ck ah +bj +cm = dg +ei +fk dh +ej +fm 2 x 3 3 x 2 2 x 2
Ex. 2 Is the product defined? 2 x 2 3 x 2 -1(4) +5(6) -1(-3) +5(8) -4 + 30 3 + 40 20 +12 -15 + 16 5(4) +2(6) 5(-3) +2(8) = 0 + -24 0 + -32 0(4) +-4(6) 0(-3) +-4(8) 26 43 32 1 -24 -32
STOP HERE for WEB!! Or look at more examples …..
Ex. 3 FindAB -16 + 1 -12 +2 -15 -10 = 0 - 2 0 - 4 -2 - 4
Ex. 4 FindBA
Ex. 5 4 x 3 3 x 1 4 x 1
Ex. 6 2 x 3 3 x 3
Homework • Page 211: #4-20 ALL • Don’t work #10