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Question

I have my exam in 20minutes and I still don't know how to multiply two matrices with different dimensions, please help!

Answer 1

Two matrices can only be multiplied if the number of COLUMNS in the first matrix equals the number of ROWS in the second matrix. The result will be a matrix with the same number of rows as the first matrix and the same number of columns in the second matrix.

Now for the element in the first row, first column of the answer [x(1,1)] take each element in the first row of the first matrix and multiply it to the corresponding element in the first column of the second matrix

[a(1,1)]*[b(1,1)]
[a(1,2)]*[b(2,1)]
[a(1,3)]*[b(3,1)]
etc

Now add those answers together and the result is the value you should put in the first row, first column of the answer matrix [x(1,1)]. Repeat for all other elements

A good example can be found here
http://www.math.utoronto.ca/mathnet/plain/questionCorner/matrixmul.html

Answer 2

i don't know if icn help you, but perhaps i can...

if you have to multiply two matrices they mast have 2 dimensionm in common .
for example: (2*3) *(3*4)=(2*4)
or : (2*3)*(3)=(2*1)==(2)

so you have to multiply the first number of the first line with the first number of the first colume. at the new number that you will gain you must add the result that you gain when you will multiply the 2nd number of the 1rst line with the second number of the 1rst colume.....etc.=>
doing that you will have o new matrice were the dimention that the two matrices have in common will be disapeared!


4 5 3 1 3 4*1+5*2+3*2 4*3+5*5+3*1 20 40
6 2 1 * 2 5 = 6*1+2*2+1*2 6*3+2*5+1*1 = 12 29
4 3 1 2 1 4*1+3*2+1*1 4*3+3*5+1*1 11 28

(i dont know if i manage to help you, but i will be glad if i could)

Answer 3

matrix

Click on the URL below for additional information concerning matrix

www.sosmath.com/matrix/matrix.html

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