TriangleFacts msabdeljalil 1

Attempt 1
This indirection saved a little text, and abstracting to `trig_function` is a nice improvement, but could you unroll this and be even clearer?

```
angle_a = trig_function(b, c, a)
angle_b = trig_function(a, c, b)
angle_c = trig_function(a, b, c)
[angle_a, angle_b, angle_c]
```

Also, not sure _which_ trig function it is, so that name may warrant some improvement.