# Homework Help: Rates of change

1. Oct 12, 2011

### Nitrate

1. The problem statement, all variables and given/known data
1. An oil tanker springs a leak creating a circular oil slick that grows until its radius is 3.0 km.

a.) What is the formula describing the relation between the area of the slick and its radius?

2. Relevant equations
Area of a circle: (pi)r^2

3. The attempt at a solution
Is the equation for a) y = (pi)r^2,
or is it the derivative: y = 2(pi)r?

2. Oct 12, 2011

### vrmuth

I think you mean the difference between the RATE OF CHANGE of the area of the slick and that of the radius , please make it clear .

3. Oct 12, 2011

### HallsofIvy

The formula you give $A= \pi r^2$ relates the area of a circle to its radius. There is nothing said in your problem, at least the part you posted, about rates of change.