 Let's do a few circle area problems. Here is the formula for finding the area of a circle: 
Visit this page to see where the formula comes from. Review π here. Example 1: Find the area 
r is the radius A = π r2 A = π (6)2 use the π button on your calculator A = 113.1 mm2 rounded to 1 d.p. Example 2: Let's double the radius and find the new area: 
A = π r2 A = π (12)2 A = 452.4 mm2 rounded to 1 d.p. Doubling the radius made the area 4 times larger because the radius is squared; 'twice' squared is 'times 4' Example 3: Finding the radius 
The area is 415.5 cm2; Find the radius:A = π r2 415.5 = π r2 415.5/π = r2 132.26 = r2 now do a square root: 11.5 cm = r Example 4: find the area 
A = π r2 The formula uses 'r', so we need to use the radius 23: A = π (23)2 A = 1661.9 cm2 Example 5: find the diameter 
The area is 1000 m2. Find the diameterThe formula uses 'r', so we'll need to solve for 'r' first: A = π r2 1000 = π r2 1000/π = r2 318.31 = r2 17.84 = r so the diameter d = 2 x 17.84 = 35.7 m |