Sage (through Pynac and GiNaC) automatically evaluates `sin(pi/6)`

, `cos(pi/6)`

, `tan(pi/6)`

:

```
sage: sin(pi/6)
1/2
sage: cos(pi/6)
1/2*sqrt(3)
sage: tan(pi/6)
1/3*sqrt(3)
```

For the comparison, it checks if `tan(pi/6) - sin(pi/6)/cos(pi/6)`

is 0:

```
sage: t = tan(pi/6) - sin(pi/6)/cos(pi/6)
sage: t
0
sage: t.is_trivial_zero()
True
```

For `pi/5`

, `tan()`

and `sin()`

are left unevaluated, while `cos()`

is:

```
sage: tan(pi/5)
tan(1/5*pi)
sage: sin(pi/5)
sin(1/5*pi)
sage: cos(pi/5)
1/4*sqrt(5) + 1/4
```

This makes the difference `tan(pi/5) - sin(pi/5)/cos(pi/5)`

a symbolic expression not trivially equal to `0`

:

```
sage: t = tan(pi/5) - sin(pi/5)/cos(pi/5)
sage: t
-4*sin(1/5*pi)/(sqrt(5) + 1) + tan(1/5*pi)
sage: t.is_trivial_zero()
False
sage: t.n()
1.11022302462516e-16
```

Any patches to improve this behavior would be more than welcome.