Properties of tangent lines are one of the concepts covered on the new SAT. Look at line GJ. It touches the circle at only one point, F. At the point where a tangent touches a circle, the tangent line is perpendicular to the circle.
Whenever a tangent hits a circle, it creates a right angle with a radius of the circle. Earn some brownie points and think of what the SAT could do with this fact. Draw a dotted line from G to C, and draw another from J to C. What you get is two right triangles.
以上是美国一个培训SAT考试(高中升大学)的网站对切线的解释。也就是说第11题里的perpendicular to the circle是指圆的切线。我做题的时候也是直觉觉得是切线而不是直径。
Properties of tangent lines are one of the concepts covered on the new SAT. Look at line GJ. It touches the circle at only one point, F. At the point where a tangent touches a circle, the tangent line is perpendicular to the circle.
Whenever a tangent hits a circle, it creates a right angle with a radius of the circle. Earn some brownie points and think of what the SAT could do with this fact. Draw a dotted line from G to C, and draw another from J to C. What you get is two right triangles.
以上是美国一个培训SAT考试(高中升大学)的网站对切线的解释。也就是说第11题里的perpendicular to the circle是指圆的切线。我做题的时候也是直觉觉得是切线而不是直径。
仅供大家参考。
感谢evelyn2005的细心搜索，看来是我对line is perpendicular to the circle的理解错误，这条line应理解为切线。
A line that has exactly one point in common with a circle is said to be tangent to the circle, and that common point is called the point of tangency. A radius or diameter with an endpoint at the point of tangency is perpendicular to the tangent line, and, conversely, a line that is perpendicular to a diameter at one of its endpoints is tangent to the circle at that endpoint.
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发表于 2006-1-14 09:30:00
