We have:\(V_{hinhcau}=3S_{hinhcau}\)

\(\Rightarrow\dfrac{4}{3}.\pi.r^3=3.4.\pi.r^2\) with \(r\) is the radius of this certain

\(\Rightarrow\dfrac{r^3}{r^2}=\dfrac{3.4.\pi}{\dfrac{4}{3}.\pi}=\dfrac{3.4}{\dfrac{4}{3}}=\dfrac{3.4.3}{4}=9\)

\(\Rightarrow r=9\)

We have:Vhinhcau=3Shinhcau

⇒43.π.r3=3.4.π.r2

 with r

 is the radius of this certain

⇒r3r2=3.4.π43.π=3.443=3.4.34=9

⇒r=9