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标题: 数学题啊~~~~~sos [打印本页]

作者: chriswendy35 时间: 2010-8-17 06:51 标题: 数学题啊~~~~~sos

a certain area has its center at point p and has radius 4, and point x and y lie in the same plane as the circular area. does point y lie outside the circul area?
(1)the distance between p and x is 4.5
(2)the distance between x and y is 9

我的理解是只要XY>9,且X在圆上，那么Y必然不在圆上，因为圆上最大距离，即圆的直径为8。
可是答案是C，迷惑了
猜测是不是lie in the same plane as the circular area没能理解，请高手指教

作者: bettytons 时间: 2010-8-17 19:45

1) insufficient b/c it gives us no information on point Y.
2) insufficient b/c it gives us no information on whether any of the two points are located inside or outside the circle.

together:

we know point x is outside the circle, (distance of 0.5 away from the point ON the circle).

xy = 9

the diameter of the circle is 8, which means the largest distance covered and the point y can still be covered inside the circle is 8.

4.5 + 4 = 8.5 (can be the maximum distance allowed for xy for y to still be a part inside the circle).

Therefore point y will lie outside the circle.

作者: banglixing 时间: 2010-8-18 06:32

题目问你Y是不是在圆的外面？那么y在圆的里面和外面都成立。

(1)不能得出y的位置，只能知道x在圆外。
(2)单独不成立，因为你不知道x的位置，所以更无法知道y的位置。

二者结合可知y不在圆内。

作者: chriswendy35 时间: 2010-8-18 20:13

题目问你Y是不是在圆的外面？那么y在圆的里面和外面都成立。

(1)不能得出y的位置，只能知道x在圆外。
( ...
banglixing 发表于 2010-8-18 06:32

“point x and y lie in the same plane as the circular area.”
是不是说X,Y 相对于圆对称？如果对称的话，X不在圆，XY距离又大于了最大直径8，那么y就不在圆上了啊？

作者: zongzeng90 时间: 2010-8-19 06:44

same plane 是指在一个平面内楼主想多了就是把圆和两个点定在一个平面内防止你考虑空间几何的可能性

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