Area or circumference of a circle
CONCEPTS
Figures
• Perimeter: length of the line around the outside of the figure (units = m, cm, in, ft).
• Circumference: same a perimeter, but for a circle
• Area: the interior space of shape in 2 dimensions (units = m², cm², in², ft²)
• Volume: the interior space of shape in 3 dimensions (units = m³, cm³, in³, ft³)
Circles
• Circumference = 2 π r (r = radius)
• Area = π r² (r = radius)
• r = 1/2 * d (r = radius, d = diameter)
PRACTICE PROBLEMS
Question 1 The diameter of a circle is 6 in. What is the area? What is the circumference?
-- Answer -- 6 π in
A=9 π in², C = 6 π in
Question 2 The circumference of a circle is 40π. What is the area?
-- Answer -- 400 π
r = 20
Area = π * 20² = 400 π
Question 3 The area of a circle is 25π. What is the circumference?
-- Answer -- 10 π
A = 25 π = π r², r = 5
C = 2 π r = 2 * π * 5 = 10 π
ACT PRACTICE PROBLEMS
