HOW TO MULTIPLY MATRICES

When we multiply two matrices, it is important to consider the dimension of matrices.

When the product of two matrices is defined ?

When the number of columns of the first matrix and number of columns in the second matrix they are equal, then the product of two matrices is defined.

When the product of two matrices is not defined ?

When the number of columns of the first matrix and number of columns in the second matrix they are not equal, then the product of two matrices is not defined.

Find each product, if possible.

Problem 1 :

3-5 .35-20

Solution:

  • Dimension of first matrix is 1 x 2
  • Dimension of second matrix is 2 x 2
  • The product is defined and dimension of product matrix will be 1 x 2.
=3-5 .35-20=(3)(3)+(-5)(-2)(3)(5)+(-5)(0)=9+1015+0=1915

Problem 2 :

58 .3-14

Solution:

  • Dimension of first matrix is 2 x 1
  • Dimension of second matrix is 1 x 3
  • The product is defined and dimension of product matrix will be 2 x 3.
=58 .3-14=5(3)5(-1)5(4)8(3)8(-1)8(4)=15-52024-832

Problem 3 :

5-2-1803 .-4210

Solution :

  • Dimension of first matrix is 2 x 3
  • Dimension of second matrix is 2 x 2
  • The product is not defined since the number of columns in the first matrix and number of rows in the second matrix is not equal.

It is not possible.

Problem 4 :

4-135 .74

Solution:

  • Dimension of first matrix is 2 x 2
  • Dimension of second matrix is 2 x 1
  • The product is defined and the order of the product matrix is 2 x 1.
=4-135 .74=4(7)+(-1)(4)3(7)+5(4)=28-421+20=2441

Find each product, if possible.

Problem 5 :

2-1 .54

Solution:

  • Dimension of first matrix is 1 x 2
  • Dimension of second matrix is 2 x 1
  • The product is defined and the order of the product matrix is 1 x 1.
=2-1 .54=2(5)+(-1)(4)=10-4=6

Problem 6 :

3-251 .4127

Solution:

  • Dimension of first matrix is 2 x 2
  • Dimension of second matrix is 2 x 2
  • The product is defined and the order of the product matrix is 2 x 2.
=3-251 .4127=12-43-1420+25+7=8-112212

Problem 7 :

4-1615-8 .139-6

Solution:

  • Dimension of first matrix is 2 x 3
  • Dimension of second matrix is 2 x 2
  • The product is not defined.

Problem 8 :

4-2-7635 .-253

Solution:

  • Dimension of first matrix is 2 x 3
  • Dimension of second matrix is 3 x 1
  • The product is defined and the order of product matrix is 2 x 1.
=4-2-7635 .-253=-8-10-21-12+15+15=-3918

Problem 9 :

2-134 .3-9-257-6

Solution:

=2-134 .3-9-257-6=6-5-18-7-4+69+20-27+28-6-24=1-252291-30

Problem 10 :

730255 .-2143-52431

Solution:

It is not possible.

Problem 11 :

40-37-59 .64-21

Solution:

=40-37-59 .64-21=24-016+0-18-14-12+7-30-18-20+9=2416-32-5-48-11

Problem 12 :

0831-15 .31-208-5

Solution:

=0831-15 .31-208-5=0+00+640-409+03+8-6-5-3+0-1+402-25=064-40911-11-339-23

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