1 | initial version |

Works for me (Sagemath 8.7):

```
sage: (cos(x)^2-1).simplify_trig()
-sin(x)^2
```

similarly :

```
sage: (sin(x)^2/(1-cos(x)^2)).simplify().simplify_trig()
1
sage: (sin(x)^2/(1-cos(x)^2)).simplify_trig()
1
```

Note that:

```
sage: (cos(x)^2-1).trig_reduce()
1/2*cos(2*x) - 1/2
```

might be more useful...

What are you using ?

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