linera solver and cas

[hpfx]

Hi,
happy new year !

I know there is a linear solver app, but it's limited to number, and I wanted to see how I can play with cas with linear system.
system is :
2x-a*y=2
-x-2y=-1
I typed linsolve([2*x-a*y=2 -x-2*y=-1],[x y])
and cas gave me : [1 0]
But expected result was -1/(2+a) and (a+4)/(a+2)


Ok... let's try with solve() that is a little bit the swiss knife of cas.
first of all, lets try with a basic system :
solve(3*x+2*y=1 AND 3*x-y=2 , {x,y})
return {[5/9 -1/3]} which is correct !
I was very enthousiatic!

then I tried :
solve(2*x-a*y=2 AND -x-2*y=-1, {x,y})
but I got {[1 0]}

something look wrong, any idea ?