title: Mathematica integral evaluation just shows up as nicely formatted text?
body: <p>Attempting the following exponential integral:</p>
  
  <pre><code>Integrate[  Exp[-2 A Sqrt[x^2 + a^2] + I ( x Subscript[k, x] + b )],
              {x, 0,   Infinity}
  ]
  </code></pre>
  
  <p>I get back something that is pretty printed, but not evaluated?  Does this mean that Mathematica could not perform the integral and gave up?  I don't see any messages saying that's what happened.</p>
  
  <p>To provide context for this question, this is a stripped down to one dimension version of the integral I'd done with paper and pencil:</p>
  
  <pre><code>\int d^3 r e^{ i \vec{k} \cdot \vec{r} } e^{ - 2 Z r/ a_0 }
  </code></pre>
  
  <p>The point of trying mathematica was to see if I could verify my result:</p>
  
  <pre><code>16 \pi Z a_0^3/(4 Z^2 + k^2 a_0^2)^2
  </code></pre>