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  • 三角形ABC中,角C=90度,AC=BC,點(diǎn)P在射線AB上運(yùn)動(dòng)(點(diǎn)P不與點(diǎn)A、B重合),PE垂直于AC于點(diǎn)E,PF垂直BC于點(diǎn)F,點(diǎn)O為邊AB的中點(diǎn),連接OE,OF.

    三角形ABC中,角C=90度,AC=BC,點(diǎn)P在射線AB上運(yùn)動(dòng)(點(diǎn)P不與點(diǎn)A、B重合),PE垂直于AC于點(diǎn)E,PF垂直BC于點(diǎn)F,點(diǎn)O為邊AB的中點(diǎn),連接OE,OF.
    (1)若點(diǎn)P在線段AB上時(shí),如圖1,判斷線段OE與OF的數(shù)量關(guān)系和位置關(guān)系,請(qǐng)直接寫(xiě)出結(jié)論,不必說(shuō)明理由.
    (2)若點(diǎn)P在線段AB的延長(zhǎng)線上時(shí),如圖2,連接PC,
    第一,判斷線段PC與OE的數(shù)量關(guān)系,并加以說(shuō)明.
    第二,判斷線段AP\BP與CP三者間的數(shù)量關(guān)系(用等式表示),直接寫(xiě)出結(jié)論.
    數(shù)學(xué)人氣:105 ℃時(shí)間:2020-02-06 06:36:05
    優(yōu)質(zhì)解答

    (圖1、2性質(zhì)相同,因此只作一圖分析)

           (1)結(jié)論:OE=OF,且OE⊥OF;

               方法:連接OC;

                         由于點(diǎn)E、F分別為過(guò)點(diǎn)P所作射線AC、CB上垂線的垂足,且點(diǎn)E、F隨點(diǎn)P的運(yùn)動(dòng)而運(yùn)動(dòng),那么點(diǎn)E、F的運(yùn)動(dòng)速率相等,則EA=FC;

                         ∵AC=BC,∠C=90°,且點(diǎn)O為線段AB的中點(diǎn);

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

                         ∵OA=OC,∠A=∠CFO,EA=FC(兩邊及其夾角相等推證全等);

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

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

           (2)①判斷:PC=√2OE;

                   分析:依題意推知,四邊形CEPF為矩形,那么PC=EF;又OE=OF,且OE⊥OF,即△EOF為等腰直角三角形,則EF=√2OE,即有PC=√2OE;

                ②判斷:AP²+BP²=2CP²;

                   分析:在Rt△PFC中,由勾股定理得

                                 CP²=FP²+CF²

                             根據(jù)題意并結(jié)合圖形可知:FP=FB=√2/2•BP;

                                                                       CB=CA=√2/2•AB;

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

                                                                       AB=AP-BP;

                   轉(zhuǎn)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.

    .

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