### Home > INT2 > Chapter 8 > Lesson 8.4.1 > Problem8-81

8-81.
1. 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. Homework Help ✎

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

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

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

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

For a circle, area = r2 · π.

area = 102·π = 100π units2

For a circle, circumference = d·π.

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

r = 11 units
What is the diameter?

Use the circumference formula and solve for the diameter.