Check if this is right plz , Matrices .

[Ahmooosh]

For matrices , when is it that we add the end result together ?

example
(2) X (1 4)

answer is

( 2x1 2x4)

(2 8)

do we add them ? like answer = 10 ? or no? is there other situations when to add them together?

 

[Nibz]

Have a look at this!

and remember this rule: To multiply matrices, the columns in the first matrix must equal the no. of rows in the second one!

 

[Ahmooosh]

yea i understand that bit , but in paper 2 , there was this question in last page , matrices ... which i got wrong , and my friends told me i should have added
(-12
12 )

to get the answer which was 0 , i am not sure if this is right , and if there is other situations where we add the end result.

so please help me out here

 

[Ahmooosh]

guys please , i really need this before my exam.

 

[burndtjamb]

In that case the number of rows in the first matrix was one, and the number of columns in the second was also one. So the result should have been a 1X1 matrix.

 

[Ahmooosh]

oh okay , so whenever the result should be a 1x1 matrix , i add the numbers i have ? even if they were next to each other?
because in p2 , the numbers were on top ,and the answer was to add the 2 numbers together. So i would like to know what would happen if they were next to each other instead.

but thanks for that man

 

[burndtjamb]

It all has to do with the way you multiply matrices. When multiplying a 2X2 matrix by another 2X2 matrix you would multiply the first number in the first row of the first matrix by the first number in the first column in the second matrix. You would do the same thing with the second number in the first row of the first matrix, except multiplying it by the second number of the first column of the second matrix. You would then add these two products together to get the first number in the product matrix.

When multiplying a 1X2 matrix by a 2X1 matrix, there is only one row and one column to use this method with. The same method is used, but you only can get one result and hence the resulting matrix is 1X1.

 

[Ahmooosh]

What would happen if multiplying 1x1 matrix and 1x2 matrix , example

( 2 ) x ( 3 4 )

would the answer be ( 6 --- 8 )
or ( 14 ) ??

thanks in advance , god be with us for maths exam....

 

[Ahmooosh]

Guys please someone answer this , i really need it for tomm

 

[burndtjamb]

the answer would be ( 6 8 )

To find out the order of the product put the order of the two matrices you are multiplying side by side

e.g. from your example 1X1 1X2

Look at the numbers on the edges (the first number in the first order and the second number in the second order)

Put them together and you will have: 1X2
That is the order you should expect when multiplying them. It will have the same number of rows as the first matrix and the same number of columns as the second matrix.

 

[Ahmooosh]

thanks man , owe u one!