title: get sympy result as trig function rather than complex log
body: <p>I'm doing some manipulation of trig equations and would like the results back in trig form.</p>
  
  <p>What I'm doing is this:</p>
  
  <pre><code>from sympy import *
  B,D,a=symbols(r'B,D,alpha',real=True,positive=True)
  eq1=Eq(D,B*((sin(a)*sin(a))/(sin(a+a))))
  solve(eq1,a)
  </code></pre>
  
  <p>I expect the result to be <code>atan(2*D/B)</code> but I'm getting:</p>
  
  <pre><code>[-I*log(-sqrt((B + 2*I*D)/(B - 2*I*D))), -I*log((B + 2*I*D)/(B - 2*I*D))/2]
  </code></pre>
  
  <p>I know sympy is expanding the trig functions into exponential form, but I can't seem to convince it to convert the results back.</p>
  
  <p>I've tried:</p>
  
  <pre><code>[n.rewrite(atan) for n in solve(eq1,a)]
  </code></pre>
  
  <p>but I get the same result back...</p>