每日一题

Mathematics>Standard Multiple Choice

Read the following SAT test question and then click on a button to select your answer.

In the figure above, inscribed triangle ABC is equilateral. If the radius of the circle is r, then the length of arc AXB is_______

(A) 2πr/3
(B) 4πr/3
(C) 3πr/2
(D) πr²/3
(E) 2πr²/3

答案和解析

答案：A

解析：

An equilateral triangle has three equal sides, so the lengths of the three arcs must be equal, and thus each arc is 1/3 of the circumference of the circle. The circumference of the circle is 2πr, so the length of arc AXB is 1/3 of 2πr, or 2πr/3.