Solve an equation in $mathbb{R}^+$

How can I solve this equation (both numerically and literally) only in the positive reals $\mathbb{R}^+$?

Solve[x == (v0 - (A CD t v0^2 ρ)/(4m)) Cos[θ] t, t]

And for example, is there a way to have an output like this :

52.0756

and not like this :

{{t -> -52.3918}, {t -> 52.0756}}

?

Answer

You could use ReplaceAll (i.e. /.) and Select

Select[x /. Solve[x^2 - 1 == 0, x], Positive]

gives

{1}

It is a list (List) not a single number. You might not know how many positive solutions exist:

Select[x /. NSolve[(x - 1) (x + 3) (x - 3) == 0, x], Positive]

{1., 3.}

Edit:

Using Part or its short-hand notation [[]] you can select parts from the list:

Part[{1}, 1]

1

{1}[[1]]

1

Part[{1.,3.},2]

3.