SOLUTION: Solve the matrix equation: {{{(matrix(2,2,4,-5,1,2))(matrix(2,1,m,n))}}}{{{""=""}}}{{{(matrix(2,1,32,-5))}}} please show work...I'm stuck on this and cannot figure out what to

Algebra ->  Matrices-and-determiminant -> SOLUTION: Solve the matrix equation: {{{(matrix(2,2,4,-5,1,2))(matrix(2,1,m,n))}}}{{{""=""}}}{{{(matrix(2,1,32,-5))}}} please show work...I'm stuck on this and cannot figure out what to      Log On


   



Question 710737: Solve the matrix equation:
%28matrix%282%2C2%2C4%2C-5%2C1%2C2%29%29%28matrix%282%2C1%2Cm%2Cn%29%29%22%22=%22%22%28matrix%282%2C1%2C32%2C-5%29%29
please show work...I'm stuck on this and cannot figure out what to do..thanks

Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!

This is really the matrix abbreviation for the system of equtions:  

system%284m-5n=32%2Cm%2B2n=-5%29

%28matrix%282%2C2%2C4%2C-5%2C1%2C2%29%29%28matrix%282%2C1%2Cm%2Cn%29%29%22%22=%22%22%28matrix%282%2C1%2C32%2C-5%29%29

Now we need to find the inverse of the coefficient matrix

%28matrix%282%2C2%2C4%2C-5%2C1%2C2%29%29

To find the inverse of a 2x2 matrix:

1. Interchange the upper left and lower right elements:

%28matrix%282%2C2%2C2%2C-5%2C1%2C4%29%29

2. Multiply the upper right and lower left elements by -1:

%28matrix%282%2C2%2C2%2C5%2C-1%2C4%29%29

3. Find the determinant of this matrix:

abs%28matrix%282%2C2%2C2%2C5%2C-1%2C4%29%29%22%22=%22%22%282%29%284%29-%285%29%28-1%29%22%22=%22%228%2B5%22%22=%22%2213

4. Divide every element of %28matrix%282%2C2%2C2%2C5%2C-1%2C4%29%29 by this value:

%28matrix%282%2C2%2C2%2F13%2C5%2F13%2C-1%2F13%2C4%2F13%29%29

That is the inverse of the coefficient matrix.

Left-multiply both sides of the matrix
equation:

%28matrix%282%2C2%2C4%2C-5%2C1%2C2%29%29%28matrix%282%2C1%2Cm%2Cn%29%29%22%22=%22%22%28matrix%282%2C1%2C32%2C-5%29%29

by the inverse of the coefficient matrix:

%22%22=%22%22

Since matrix multiplication is associative, we can move
the parentheses from around the 2nd and 3rd matrices
on the left to around the 1st and 2nd matrices on the
left:

%22%22=%22%22

Now we multiply the two matrices on the far
left and the far right:  

%22%22=%22%22

Simplify:

%22%22=%22%22%28matrix%282%2C1%2C64%2F3-25%2F13%2C-32%2F13-20%2F13%29%29%0D%0A%0D%0A

%22%22=%22%22%28matrix%282%2C1%2C39%2F13%2C-52%2F13%29%29%0D%0A%0D%0A

%22%22=%22%22%28matrix%282%2C1%2C3%2C-4%29%29%0D%0A%0D%0A

Multiply the matrices on the left:

%28matrix%282%2C1%2C1%2Am%2B0%2An%2C+0%2Am%2B1%2An%29%29%22%22=%22%22%28matrix%282%2C1%2C3%2C-4%29%29 

Simplify:

%28matrix%282%2C1%2Cm%2Cn%29%29%22%22=%22%22%28matrix%282%2C1%2C3%2C-4%29%29 

So the solution is 

m=3, n=-4

Edwin