Mathematics for IGCSE & O level - Mensuration (Section 2 - No. 35)
If the radius of a sphere is tripled, how does its surface area change?
It triples.
It is multiplied by 6.
It increases by a factor of 9.
It is halved.
Giải thích
Surface area = 4πr². If r is tripled, surface area = 4π(3r)² = 36πr²= 9 x (4πr²)