### SImply Trigonometric Equation solving

I was a MapleV user in the past (~25 years ago) an I'm very pleased to find such an elegant solution the sage is.
I try to see how it works trying to solve an easy trigonometry calculation:

```
var('r,l,m')
ex = l/sin(m/2/r)-r
solve(ex,r)
[r == l/sin(1/2*m/r)]
```

Do not want, ok. To simplify I put some real values m and l and tried again:

```
exval = ex.subs(l=7.2,m=10)
solve(exval,r)
[r == 36/5/sin(5/r)]
```

still not solving, r=3.68357 is what I'm searching for. What would be a right way to proceed?
Thank you in advance, v42