# I cannot take sqrt of units

I'm trying to use sagemath to evaluate equations that involve units. And when I hit a `sqrt`

of a unit it won't evaluate it.

For example:

```
sage: sqrt(4*units.length.meter^2)
2*sqrt(meter^2)
```

The result should be `2*meter`

but I can't figure out how to force it to evaluate the sqrt of m^2. Even if I try to convert it like:

```
(sqrt(4*units.length.meter^2)).convert(units.length.meter)
```

I get:

```
ValueError: Incompatible units
```

Like this

Thanks. That does actually get me 1 step further. But this was a stripped down version of my overall equation. I now have another pesky part of the equation to deal with:

In some simpler equations

`polynomial(RR)`

helps. Is there something I'm doing wrong here constructing and evaluating these equations?I can do a similar thing in Mathematica and it allows me to call

`N[]`

and it reliably gives me back 1 number and a unit.Another alternative (after canonicalizing the radical) is to use an ExpressionTreeWalker to substitute numerical approximations (that should probably be built-in functionality, hidden inside a new method).