Four Fours/81

Puzzle

Using exactly $4$ instances of the number $4$, the task is to write an expression for $81$, using whatever arithmetical operations you consider necessary.

Solutions

Solution $1$

$81 = \dfrac 4 {. \dot 4} \times \dfrac 4 {. \dot 4}$

Solution $2$

$81 = \paren {\dfrac 4 {. \dot 4} }^{\tfrac 4 {\sqrt 4} }$

Also see

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