Answer:
452.4 cm^2
Step-by-step explanation:
Use the area formula A = πr². With d = 24 cm, r = 12 cm, and so the desired area is
A = π(144 cm^2) = 452.4 cm^2
2, he answer is 2 do not question my answer
Answer:
The rate of change in surface area when r = 20 cm is 20,106.19 cm²/min.
Step-by-step explanation:
The area of a sphere is given by the following formula:

In which A is the area, measured in cm², and r is the radius, measured in cm.
Assume that the radius r of a sphere is expanding at a rate of 40 cm/min.
This means that 
Determine the rate of change in surface area when r = 20 cm.
This is
when
. So

Applying implicit differentiation.
We have two variables, A and r, so:



The rate of change in surface area when r = 20 cm is 20,106.19 cm²/min.
3.174 is closer to 3.2 because, when rounding, 0.07 rounds up to 0.2.