##8##

Use the formula for the area of a circle:

##A=pir^2##

Here, the area is ##16pi##:

##16pi=pir^2##

Divide both sides by ##pi##:

##16=r^2##

Take the square root of both sides:

##sqrt16=sqrt(r^2)##

##4=r##

Since the radius of the circle is ##4##, the diameter is twice that:

##d=4xx2=8##

##8##

Use the formula for the area of a circle:

##A=pir^2##

Here, the area is ##16pi##:

##16pi=pir^2##

Divide both sides by ##pi##:

##16=r^2##

Take the square root of both sides:

##sqrt16=sqrt(r^2)##

##4=r##

Since the radius of the circle is ##4##, the diameter is twice that:

##d=4xx2=8##