2014年7月9日
Read the following SAT test question and then click on a button to select your answer.
In the figure above, the circle with center 
and the circle with center 
are tangent at point 
. If the circles each have radius 
, and if line 
is tangent to the circle with center 
at point 
, what is the value of 
?
A. 
B. 
C. 
D. 
E. It cannot be determined from the information given.
| 正確答案:B 解析: The circles each have radius |
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, so 
. Since the circles are tangent at point 
, segment 
contains 
and 
. 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 
and side 
of length 
. A right triangle with one side of length one-half that of its hypotenuse is a 
triangle. The 
angle is opposite side 
, so 
.