Answer:
c. 
Step-by-step explanation:
We have been given that the area in square units of an expanding circle is increasing twice as fast as its radius in linear units
We will use derivatives to solve our given problem.
We know that area (A) of a circle is equal to
.
Let us find derivative of area function with respect to time.

Bring out constant:

Using power rule and chain rule, we will get:

Here
represents change is radius with respect to time.
We have been given that area of an expanding circle is increasing twice as fast as its radius in linear units. We can represent this information in an equation as:





Therefore, the radius is
and option 'c' is the correct choice.
I would help you but I’m trying to do my hw too srry maybe next time
Answer:
--- small circle
--- big circle
Step-by-step explanation:
Given
-- sum of areas

Required
The radius of the larger circle
Area is calculated as;

For the smaller circle, we have:

For the big, we have

The sum of both is:


Substitute: 


Substitute 

Factorize
![80\pi = \pi[ r^2 + 4r^2]](https://tex.z-dn.net/?f=80%5Cpi%20%3D%20%5Cpi%5B%20r%5E2%20%2B%204r%5E2%5D)
![80\pi = \pi[ 5r^2]](https://tex.z-dn.net/?f=80%5Cpi%20%3D%20%5Cpi%5B%205r%5E2%5D)
Divide both sides by 

Divide both sides by 5

Take square roots of both sides


The radius of the larger circle is:


