(a-b)? =a？ -2ab+b？ ≥0

Answer? +b？ ≥2ab

Similarly, a+b≥√a * √b=√(ab) a≥0, b≥0 When a=b, the equation holds.

Now 25/R+R ≥ √ (25/R) * √ R = √ (25/R * R) = √ 25 = 5 When 25/R=R, the equation holds.

That is, when R=5, there is a minimum value, and its minimum value is 5.