The formula for the surface area of a sphere is a = 4πr2. what is the formula solved for r

 
_____________________________________________________________
" r =  " ;
 
or; write as:  " r =  " ; 

or; write as:  " r =  " .
________________________________________________________
Explanation:
________________________________________________________
Note the formula for the surface area, "a" ; of a sphere:

→  " a = 4 π r² " ;

→  Let us rearrange the equation to isolate "r" on one side of the equation: 

→  Given:  "  a = 4 π r² " ; 

↔  4 π r² = a ; 

Divide EACH side of the equation by " [4 * π] " ;

→    {4 π r²} / [4 * π]  = a / [4 * π] ;

to get:

→  r² =  { } ;

Now, take the POSITIVE square root of each side of the equation; 
 to isolate "r" on one side of the equation; 

→  √(r²)  = √ { } ;

→                      " r =  " ;
 
or; write as:  " r =  " ; 

or; write as:  " r =  " .
___________________________________________________________

Whose mistake? can you give more details to what the question is asking?