Four Fours/Lemmata/Three Fours/21/Solutions

Puzzle: Three Fours: $21$

Using exactly $3$ instances of the number $4$, the task is to write an expression for $21$, using whatever arithmetical operations you consider necessary.

Solutions

Solution $1$

$21 = 4! - \sqrt {\dfrac 4 {. \dot 4} }$