Find DE if D=[-2 4 6] and E=[1 -2]
[5 -7 1] [0 4]
[-3 4]
I followed the example in the book on how to multiply matrices and one I found on the Internet and keep coming up with the same answer which is not one of the solutions given to choose from.
WORK: [(-2)(1)+(4)(0)+(6)(-3)]=-20
[(-2)(-2)+(4)(4)+(6)(4)]=44
[(5)(1)+(-7)(0)+(1)(-3)]=2
[(5)(-2)+(-7)(4)+(1)(4)]=-34
I keep getting [-20 44]
[2 -34]
Answers to choose from are:
A) [20 44] B) [-20 8]
[8 42] [44 42]
I don't know where I am going wrong, so hopefully this will stay aligned and you can see where I am making my mistake!!
Thanks.
did not stay aligned so I will try something else.
I understand what you did and agree with your answer
-20__44
__2_-34
In matrix multiplication, each element in the resulting matrix is obtained by taking the dot product of the corresponding row from the first matrix and the corresponding column from the second matrix.
Let's calculate the multiplication of D and E step by step:
D = [-2 4 6] E = [1 -2]
[5 -7 1] [0 4]
[-3 4]
For the first element of the resulting matrix DE, we need to take the dot product of the first row of D and the first column of E:
(-2)(1) + (4)(0) + (6)(-3) = -2 + 0 - 18 = -20
For the second element of DE, we need to take the dot product of the first row of D and the second column of E:
(-2)(-2) + (4)(4) + (6)(4) = 4 + 16 + 24 = 44
For the third element of DE, we need to take the dot product of the second row of D and the first column of E:
(5)(1) + (-7)(0) + (1)(-3) = 5 + 0 - 3 = 2
For the fourth element of DE, we need to take the dot product of the second row of D and the second column of E:
(5)(-2) + (-7)(4) + (1)(4) = -10 - 28 + 4 = -34
Therefore, the resulting matrix DE is:
DE = [-20 44]
[2 -34]
Comparing it with the given options, the answer is not among the choices provided. It appears there may be an error in the given options or the calculation of the answer choices.