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在平面直角坐标系xoy中，已知点P（2，1），点T（t，0）是x轴上的一个动点，当△PTO是等腰三角形时，t值的个数是______．

答案

如右图所示，

①∵P点的坐标是（2，1），

∴OP=

22+12
=
5
，

∴以O为圆心，OP长为半径画弧（OP做腰），

交x轴分别是（

5
，0），（-
5
，0）；

②设T的坐标是（x，0），OP做等腰三角形的底边，那么有

(x-0)2+(0-0)2
=
(2-x)2+(1-0)2
，

即x2=4-4x+x2+1，

解得x=

5
4
，

故T的坐标是（

5
4
，0）；

③AP是等腰三角形底边的垂直平分线，那么O点的对称点坐标是（4，0）．

故t的值有4个．

选择题

2007年11月3日，中华人民共和国政府和乌兹别克斯坦共和国政府发表联合公报。双方决心在维护国家独立、主权、安全等重大问题上相互支持对方的政策和行动。双方决心在维护国家独立、主权、安全等重大问题上相互支持对方的政策和行动，因为这样做（ ）

A．符合两国共同的利益

B．有利于结成战略同盟关系

C．有利于扩大势力范围

D．有利于维护我国国家安全和利益
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