GRE考试

【单选题】

In the figure above, the radius of circle O is 3, and m∠AOB=60. What is the perimeter of the shaded region


网考网参考答案：C
网考网解析：
Since each radius is 3, OA = OB, and by KEY FACT J3 m∠A = m∠B. [*] Then, 60 + x + x = 180 [*] x = 60. Therefore ΔAOB is equilateral, and AB = 3. The length of arc AB is [*] of the circumference. C = 2π(3) = 6π, so the length of arc AB = π. The perimeter of the region, then, is 3 + π. **Use TACTIC 2, Chapter 10: trust the diagram. AB looks about the same as OB, so assume it is 3, and arc AB is clearly slightly bigger. Hence, the perimeter is a little more than 6. Choices A and B are both less than 5, which is definitely too small. Between C and D guess. C, 3 + re, is the better guess, because AB might be exactly 3. document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>