Maxima Solve question



I don't understand the following results from Solve. 

(%i4) y=2*x;

(%o4) y=2*x

(%i5) y=sqrt(x^2+3);

(%o5) y=sqrt(x^2+3)

(%i6) solve([%o4,%o5],[x,y]);

 

(%i6) solve([%o4,%o5],[x,y]);`

algsys' cannot solve - system too complicated.

 -- an error.  To debug this try debugmode(true);

 

The manual solution provides x=+/- 1. A quick look at the plot shows that
x=-1 is not valid. Why does solve have a problem?

 

Thanks

 

Ron