What to do, to make maple evaluate the limit

limit(exp(-a*x), x = infinity)

where a>0 as zero? Thank you!

Hello,

I've been trying to force maple to find a solution of this differential equation:

ode := -((D@@2)(y))(r)-2*y(r)/r+y(r) = (2-V(r))*u[0](r)

dsolve(ode, y(r));

gives

y(r) = r exp(-r) _C2 + (exp(r) + 2 exp(-r) Ei(1, -2 r) r) _C1 - 4 

            /  /  / 
            |1 | |  
  exp(-3 r) |- | |  
            |2 | |  
            \  \/   

                               /   2    \             \