On Mon, 2006-05-22 at 18:57 -0300, Henry Lenzi wrote:
> 1) Why does Maxima not accept -sqrt(something) and proceeds to do
> sqrt(-something)?
>
> (%i8) integrate(r,z,-sqrt(20-r^2),sqrt(20-r^2));
I guess you expect 20-r^2 to be positive.
> 2
> Is r - 20 positive, negative, or zero?
>
> positive;
I think you got confused here. The simplification process in Maxima
transformed your input (20-r^2) into -(r^2-20). That means you should
answer that r^2-20 is negative, to get the answer I guess you were
expecting:
2
Is r - 20 positive, negative, or zero?
negative;
2
(%o8) 2 r sqrt(20 - r )
I hope this helps,
Jaime