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Warm-Up. 3). 1). 4) Name the dimensions. 2). Quiz – you may not use your notes. 1). 3). 4) Name the dimensions. 2). Check your work!! Watch out for careless errors. 4.2 Multiplying Matrices. p. 208. In order to multiply matrices. A • B = AB. m x n. m x p. n x p.
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Warm-Up 3) 1) 4) Name the dimensions 2)
Quiz – you may not use your notes 1) 3) 4) Name the dimensions 2) Check your work!! Watch out for careless errors.
4.2 Multiplying Matrices p. 208
In order to multiply matrices... A • B = AB m xn m x p nx p Ex 1. Can you multiply? What will the dimensions be? A B AB 2 x 3 3 x 4 2 x 4 AB A B 5 x 3 5 x 2 Not possible
How to multiply... ac ad = 2 x 1 1 x 2 2 x 2
How to multiply... ac ad = bc bd 2 x 1 1 x 2 2 x 2
Ex. 2 FindAB -16 + 1 -12 +2 -15 -10 = 0 - 2 0 - 4 -2 - 4
Ex. 3 FindBA
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. 4 -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
If we are multiplying matrices, we multiply each row of the first matrix by each column in the second matrix!! multiply each row of the first matrix by each column in the second matrix!! + + 1 + + 2 + + 1 + +
2 X 3 3 X 3 2(3)+(-3)(8)+5(-3) 2(9)+(-3)(0)+ 5(1) 2(1)+(-3)(-4)+ 5(5) -1(3)+(6)(8)+8(-3) -1(9)+(6)(0)+ 8(1) -1(1)+(6)(-4)+ 8(5)