# Computing derivatives

Hey guys,

I dont know where the problem is, but sage (5.10 here) doesnt compute easy derivatives as e.g.

```
x = var('x')
f = sqrt(x)
diff(f,x)
```

This leads to the following error: TypeError: unable to simplify to float approximation

Whats the problem here?

Can you give us your *complete* session? This should work fine, it sounds like you probably accidentally defined something in-between which changed things.

That's what you'd get if `sqrt` were actually `math.sqrt` and not Sage's `sqrt`.

DSM, why don't you put your answer as an answer so pinwheel can accept it?