What is the area of the circle with a radius of 7 cm?
Hint
The formula hasn't changed. Pie are still squared.
Answer
49π ≈ 153.9 cm2
Example 2
What is the area of the circle below?
Hint
The diameter of a circle is twice the length of the radius.
Answer
25π ≈ 78.5 yd2
Example 3
What is the area of the circle below?
Hint
What if we cut the diameter in half?
Answer
1.44π ≈ 4.52 m2
Example 4
A sector has a central angle of 73° and a radius of 3. What is the area of the sector?
Hint
Use the area formula for sectors where θ = 73° and r = 3.
Answer
1.825π ≈ 5.73 units2
Example 5
A circle has an area of 6.28 square kilometers. What is the circumference of the circle?
Hint
Relating area to circumference takes two equations, both having to do with radius.
Answer
Example 6
In the National Basketball Association, NBA, the diameter of the center circle is 12 feet. In the International Basketball Federation, FIBA, the center circle's diameter is 11.81 feet. How much larger is the area of the NBA center circle as compared to the area of the FIBA center circle?
Hint
Subtract the FIBA area from the NBA area to find the difference. Oh, and don't forget that the problem gives you the diameters, not the radii.
Answer
The NBA center circle is about 3.55 ft2 larger than the FIBA center circle.
Example 7
On a basketball court, the restricted area is a semicircle beneath the basket. In the NBA, the restricted area has a radius of 4 feet. In the NCAA (college basketball), the area has a radius of 3 feet. How much larger is the restricted area of the NBA compared to that of the NCAA?
Hint
Semicircles are half-circles. We should probably modify the area and circumference formulas accordingly.
Answer
The NBA restricted area is nearly 11 ft2 larger than that in the NCAA.
