Use your findings from problem 8-79 to answer the questions below. Recall that the diameter of a circle is a segment with endpoints on the circle that passes through the center. The length of the segment is also called the diameter.

1. What is the area of a circle with radius $10$ units?

   Hint (a):

   For a circle, area $= r^2 · π$.

   Answer (a):

   area $= 10^2·π = 100π$ units^{$^2$}

2. What is the circumference of a circle with diameter $7$ units?

   Hint (b):

   For a circle, circumference $= d·π$.

3. If the area of a circle is $121π$ square units, what is its diameter?

   Hint (c):

   Use the formula for area of circle and solve for the radius.

   Partial Answer (c):

   $r = 11$ units
   What is the diameter?

4. If the circumference of a circle is $20π$ units, what is its area?

   Hint (d):

   Use the circumference formula and solve for the diameter.

   More Help (d):

   What is the radius? Use the radius to calculate the area.