> 数学 >
三角形ABC中,角C=90度,AC=BC,点P在射线AB上运动(点P不与点A、B重合),PE垂直于AC于点E,PF垂直BC于点F,点O为边AB的中点,连接OE,OF.
(1)若点P在线段AB上时,如图1,判断线段OE与OF的数量关系和位置关系,请直接写出结论,不必说明理由.
(2)若点P在线段AB的延长线上时,如图2,连接PC,
第一,判断线段PC与OE的数量关系,并加以说明.
第二,判断线段AP\BP与CP三者间的数量关系(用等式表示),直接写出结论.
人气:137 ℃ 时间:2020-02-06 06:36:05
解答

(图1、2性质相同,因此只作一图分析)

       (1)结论:OE=OF,且OE⊥OF;

           方法:连接OC;

                     由于点E、F分别为过点P所作射线AC、CB上垂线的垂足,且点E、F随点P的运动而运动,那么点E、F的运动速率相等,则EA=FC;

                     ∵AC=BC,∠C=90°,且点O为线段AB的中点;

                     ∴OA=OC,且∠A=∠OCF=45°;

                     ∵OA=OC,∠A=∠CFO,EA=FC(两边及其夹角相等推证全等);

                     ∴△AOE≌△COF,则OE=OF;

                     由于△AOE≌△COF,那么∠AOE=∠COF,而∠AOE与∠COF共∠COE,又∠AOE=∠COE+90°,则∠EOF=90°,即有OE⊥OF;

       (2)①判断:PC=√2OE;

               分析:依题意推知,四边形CEPF为矩形,那么PC=EF;又OE=OF,且OE⊥OF,即△EOF为等腰直角三角形,则EF=√2OE,即有PC=√2OE;

            ②判断:AP²+BP²=2CP²;

               分析:在Rt△PFC中,由勾股定理得

                             CP²=FP²+CF²

                         根据题意并结合图形可知:FP=FB=√2/2•BP;

                                                                   CB=CA=√2/2•AB;

                                                                   CF=CB+FB=√2/2•(AB+BP);

                                                                   AB=AP-BP;

               转化:CP²=FP²+CF²

                               =(√2/2•BP)²+½•(AB+BP)²

                               =BP²+½•AB²+AB•BP

                               =BP²+½•(AP-BP)²+(AP-BP)•BP

                               =½•(AP²+BP²)

                          故AP²+BP²=2CP².

.

推荐
猜你喜欢
© 2024 79432.Com All Rights Reserved.
电脑版|手机版