Use what you know about the area and circumference of circles to answer the questions below. Show all work. Leave answers in terms of $π$.  

1. If the radius of a circle is $14$ units, what is its circumference? What is its area?

   Hint (a):

   Remember that the area of a circle is $\pi r^2$, while the circumference of a circle is $2\pi r$.

   Answer (a):

   $\text{area} = 196\pi$
   $\text{circumference}=28\pi$

2. If a circle has diameter $10$ units, what is its circumference? What is its area?

   Hint (b):

   Use the formulas given in part (a). What is the radius of this circle?

3. If a circle has circumference $100\pi$ units, what is its area?

   Step (c):

   $100\pi = 2\pi r$
   Solve for the radius then use the radius to calculate the area.

4. If a circle has circumference C, what is its area in terms of C?

   Step 1(d):

   $C = 2\pi r$

   Step 2(d):

   $\frac{C}{2\pi} = r$

   Step 3(d):

   $A = \pi r^2 =\pi(\frac{C}{2\pi})^2$

   Step 4(d):

   $A = \frac{\pi C^2}{4\pi^2} = \:?$