Question 433993
As we know the surface area of cylinder is {{{(pi)*D*H}}}, where D is the 

diameter, and H is the height of cylinder, since H=D we can write:

{{{200=(pi)*D^2}}}, solving this equation we find {{{D=sqrt(200/(pi))}}} and 

the radius {{{R=D/2}}}, {{{R=(1/2)*sqrt(200/(pi))}}}, rationalizing we find,

{{{R=5*sqrt(2)/(sqrt(pi))=5*sqrt(2*pi)/(pi)}}}.