输血狗狗第107题讨论～～～～～大神来~~

qiaohengsdu

107. 有个求PQ值的范围AB是半径 r=5   AP=12  是切线圆心是O  Q 是左半边圆上的任意一点 ，问，PQ的长度。

解：AO ⊥AP,Ap=12，AO=5，根据勾股定理，OP应该为13

所以在ΔPOQ中，根据两边之和大于第三边，两边之差小于第三边得：

8<X<18

这个题，我觉得应该是12<Q<18这个区间里的，因为题目里说的是“左边半圆”

qiaohengsdu

sdcar2010

You are wrong. The point A is to the left of point O. The smallest value for PQ is 13-5 = 8 and Q is the point at which line PO intersects the hemicircle. The largest value for PQ is the square root of (5^2 + 17^2) = 17.8.

ClaireDawson

我也算的这个呢。。

病的希求日记

同意LZ~到时候看题目条件

myfield

楼主小心，据说这道题题干里没说在左边，到时候自己看题目吧~~加油啊

qiaohengsdu

楼主小心，据说这道题题干里没说在左边，到时候自己看题目吧~~加油啊

-- by 会员 myfield (2011/7/10 11:16:30)

谢谢，的确要小心~~你也加油哈

qiaohengsdu

You are wrong. The point A is to the left of point O. The smallest value for PQ is 13-5 = 8 and Q is the point at which line PO intersects the hemicircle. The largest value for PQ is the square root of (5^2 + 17^2) = 17.8.

-- by 会员 sdcar2010 (2011/7/10 10:36:32)

。。。你这个挺抽象的

sdcar2010

A good picture is more than a thousand words . . .

PQ1 (Blue) is the shortest length.

PQ2 (Red) is the longest length.

End of story.

chxingsh

A good picture is more than a thousand words . . .

PQ1 (Blue) is the shortest length.

PQ2 (Red) is the longest length.

End of story.

-- by 会员 sdcar2010 (2011/7/10 11:21:18)

请教楼上为啥红线是最长的啊