HI I'm really close to the answer, but do not know where I went wrong..

Consider the two equations 4x+8y=1 and 2x-ay=11 ( One is on top of the other) so in matrix form it is

=

For what values of a does the system have a unique solution?

Arranging in augmented matrix and using row operations, I reduced the matrix to

=

I had to invert the matrix premultiplied to the matrix containing x and y, so I had to get the det, I got 8a+32

=

Then I multiplied the determinant into the inversed matrix, simplified, was left with

multiplying them, I get

So my answer is x = .. and y =

but it's wrong.. can someone show me where I went wrong?

Will really appreciate it, thank you so much!