October 13th, 2012, 06:30 PM  #1 
Newbie Joined: Oct 2012 Posts: 8 Thanks: 0  Matrix inverse problem
Using the fact that the inverse of [(1 2 1), ( 2 3 1), ( 1 2 1) ] is [(8 2 5), (5 1 3), (1 0 1)] solve the following system of equations. a) x + 2y  z = 1 2x + 3y + z = 0 1x + 2y 2z = 2 x = 2, y = 1, z = 1 b) 8x + 5y +z = 3 2x y = 1 5x 3y z = 6 How do I do part b? 
October 13th, 2012, 09:07 PM  #2 
Newbie Joined: Oct 2012 Posts: 8 Thanks: 0  Re: Matrix inverse problem
Dont worry I worked it out

October 15th, 2012, 10:50 AM  #3 
Math Team Joined: Sep 2007 Posts: 2,409 Thanks: 6  Re: Matrix inverse problem
Great! For the benefit of others who are interested in this: We can write that system of equations as a matrix equation: AX= B where , the first matrix you mention, and for the first problem, for the second. Multiplying on both sides by the inverse of A, so, since you are given the inverse matrix to A, solving for x is just a matter of matrix multiplication. I bet your next problem set will require you to find the inverse matrix yourself! (However, having checked it, I need to point out that the inverse of is NOT ) 

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