Official Guide
In the racetrack shown above, regions I and III are semicircular with radius r. If region II is rectangular and its length is twice its width, what is the perimeter of the track in terms of r?
A. \(2r(\pi+2)\)
B. \(2r(\pi+4)\)
C. \(2r(\pi+8)\)
D. \(4r(\pi+2)\)
E. \(4r(\pi+4)\)
OA B
In the racetrack shown above, regions I and III are semicircular with radius r. If region II is rectangular and its...
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Solution:AAPL wrote: ↑Mon Nov 02, 2020 4:18 amOfficial Guide
2019-04-26_1746.png
In the racetrack shown above, regions I and III are semicircular with radius r. If region II is rectangular and its length is twice its width, what is the perimeter of the track in terms of r?
A. \(2r(\pi+2)\)
B. \(2r(\pi+4)\)
C. \(2r(\pi+8)\)
D. \(4r(\pi+2)\)
E. \(4r(\pi+4)\)
OA B
We see that the width of the rectangle = diameter of the semicircle = 2r, and the length of the rectangle = 4r.
The perimeter of the track consists of the circumference of one circle and twice the length of the rectangle in the middle. Therefore, the perimeter of the track is:
2πr + 2 x 4r2πr + 8r = 2r(π + 4)
Answer: B
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