sympy/sympy — pull request #1359 by Krastanov (2012-06-16 20:53:39+00:00)
Title: Evaluate trig_func(atan2) in the same manner as trig_func(atan)

Now this works:
```
In [1]: cos(atan2(y,x))
Out[1]:

x
────────────
_________
╱ 2 2
╲╱ x + y
```

As well as the cases for the other trigonometric functions.