example
A circle has radius
10 centimeters. Approximate its ⓐ circumference and ⓑ area.
Solution
ⓐ Find the circumference when r=10. |
|
Write the formula for circumference. |
C=2πr |
Substitute 3.14 for π and 10 for , r . |
C≈2(3.14)(10) |
Multiply. |
C≈62.8 centimeters |
ⓑ Find the area when r=10. |
|
Write the formula for area. |
A=πr2 |
Substitute 3.14 for π and 10 for r . |
A≈(3.14)(10)2 |
Multiply. |
A≈314 square centimeters |
example
A circle has radius
42.5 centimeters. Approximate its ⓐ circumference and ⓑ area.
Answer:
Solution
ⓐ Find the circumference when r=42.5. |
|
Write the formula for circumference. |
C=2πr |
Substitute 3.14 for π and 42.5 for r |
C≈2(3.14)(42.5) |
Multiply. |
C≈266.9 centimeters |
ⓑ Find the area when r=42.5 . |
|
Write the formula for area. |
A=πr2 |
Substitute 3.14 for π and 42.5 for r . |
A≈(3.14)(42.5)2 |
Multiply. |
A≈5671.625 square centimeters |
example
A circle has radius
1514 meter. Approximate its ⓐ circumference and ⓑ area.
Answer:
Solution
ⓐ Find the circumference when r=1514. |
|
Write the formula for circumference. |
C=2πr |
Substitute 722 for π and 1514 for r . |
C≈2(722)(1514) |
Multiply. |
C≈1588meters |
ⓑ Find the area when r=1514. |
|
Write the formula for area. |
A=πr2 |
Substitute 722 for π and 1514 for r . |
A≈(722)(1514)2 |
Multiply. |
A≈225616square meters |