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March 5th, 2010, 03:31 PM   #1
Joined: Mar 2010

Posts: 5
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Matrice Assistance


I am trying to understand what this question is asking of me in matrices & what is the format I should give the answer in:


Let A =
(1 2)
(1 -1)
B =
(2 6)
(3 -4)
C =
(3 2 )
(-2 -1)

(a) Calculate 2A - 3B + 4C.
(b) Verify that (AB)C = A(BC).
(c) Does AB = BA?
First off:
a. I do this:
A= (2 4)
(2 -2)
B = (-6 -1
(-9 +12)
C = (12 8 )
(-8 - 4)
So far am I correct?
But I give my answer by creating a new matrice called D where I have D = 2A-3B+4C
So D= (8 -6)
(-15 6)
Is this what the question a. is asking of me? And is this the correct format to give the answer(creating D)?

For b. I am unsure of what the question is asking me?
Do I have to show that (A*B)*C == A*(B*C)? So I must create a Matrice D which = (AB)C & a matrice E which = A(BC) & show that D == E? Am I on the right track or way off?

Can you clarify how to multiply 2 matrices?
If i have to multiply A*B do I do this...

A = (a1 a2) B = (b1 b2)
(a3 a4) (b3 b4)

AB = ( (a1*b1) (a2*b2) )
( (a3*b3) (a4*b4) )
Is that how to find AB or am I incorrect?
gretty is offline  
March 5th, 2010, 05:26 PM   #2
Senior Member
Joined: Apr 2008

Posts: 435
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Re: Matrice Assistance

Your first part is correct.

To check if AB*C = A*BC, multiply them out in the order indicated.

Your formula for matrix multiplication is not correct. I recommend for a very quick summary of matrix multiplication, despite the source.

jason.spade is offline  

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