Answer:
A = 9π cm²
Step-by-step explanation:
Given that area (A) varies directly with r² then the equation relating them is
A = kr² ← k is the constant of variation
To find k use the condition A = 4π when r = 2 , then
4π = k × 2² = 4k ( divide both sides by 4 )
π = k
A = πr² ← equation
when r = 3 , then
A = π × 3² = 9π cm²
