We'd start Cramer's Rule by finding D:

D = [ row 1: 1 , 3  row 2: 2 , 6 ] = 0

and we'd get stuck with

x = ( Dx / D ) = ( Dx / 0 ) and x = ( Dy / D ) = ( Dy / 0 )

           BIG TROUBLE!

So, this all ties together!

If the determinant of the coefficient matrix is zero, then the system does not have a nice ( x , y ) solution.  (Remember that the lines could be parallel, or they could be the same line.)  AND, if the determinant of a matrix is zero, then the matrix does not have an inverse...  So, we can't get a nice ( x , y ) solution!

 


YOUR TURN:

(and be sure to do a quick check on the determinant before you start in on the inverse):

Use inverse matrices to solve:

3x - 6y = 5

-4x + 8y = -1

 

Use inverse matrices to solve:

8x - 7y = 4

2x + 9y = -6