Answer:
A) 3 cm
Step-by-step explanation:
The formula of a volume of a cylinder:
[tex]V=\pi r^2H[/tex]
r - radius
H - height
We have r = 1cm and H = 21cm. Substitute:
[tex]V=\pi(1^2)(21)=21\pi\ cm^3[/tex]
The formula of a cone:
[tex]V=\dfrac{1}{3}\pi r^2H[/tex]
r - radius
H - height
We have V = 21π cm³ and H = 7cm. Substitute:
[tex]\dfrac{1}{3}\pi(r^2)(7)=21\pi[/tex] divide both sides by π
[tex]\dfrac{1}{3}(7)(r^2)=21[/tex] divide both sides by 7
[tex]\dfrac{1}{3}r^2=3[/tex] multiply both sides by 3
[tex]r^2=9\to r=\sqrt9\\\\r=3\ cm[/tex]
