The radius of a circle is tripled. By what factor is the area changed?
A) 3
B) 6
C) 9
D) 12

Question

Quizplus · Accepted Answer

The area of a circle is given by the formula A=πr².
If the radius is tripled, the new radius is 3r.
The new area can be found by substituting 3r for r in the formula for the area:

A' = π(3r)² = π(9r²) = 9πr²

Therefore, the new area is 9 times the original area, which means it is increased by a factor of 9. 
Thus, the correct answer is (C).

The Radius of a Circle Is Tripled