SAT I 每日一问:2012年7月11日
作者:沪江英语
来源:Collegeboard
2012-07-11 13:52
The correct answer is B
Explanation
The circles each have radius 10, so AB=AD=DC=10. Since the circles are tangent at point D, segment contains D and AC=20. Also, and are perpendicular because a line tangent to a circle forms a right angle with the radius at the point of tangency. Therefore, is a right triangle with hypotenuse 20 and side of length 10. A right triangle with one side of length one-half that of its hypotenuse is a triangle. The angle is opposite side , so x=90-30=60.