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March 5th, 2010, 03:31 PM   #1
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Matrice Assistance

Hello

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

Quote:
 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:
Quote:
 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
Quote:
 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...

Quote:
 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?

 March 5th, 2010, 05:26 PM #2 Senior Member   Joined: Apr 2008 Posts: 435 Thanks: 0 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 http://en.wikipedia.org/wiki/Matrix_(mathematics) for a very quick summary of matrix multiplication, despite the source. Sufficient?

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