北師大版八年級(jí)下冊(cè)《第1章 三角形的證明》同步練習(xí)卷A（6）

1、北師大版八年級(jí)下冊(cè)第1章 三角形的證明2014年同步練習(xí)卷a（6）一、選擇題（共7小題，每小題3分，滿分21分）1如果三角形的三個(gè)內(nèi)角度數(shù)比為1：1：2，則這個(gè)三角形為（）a銳角三角形b鈍角三角形c非等腰直角三角形d等腰直角三角形顯示解析2下面命題不正確的是（）a兩個(gè)內(nèi)角分別是50和65的三角形是等腰三角形b兩個(gè)外角相等的三角形是等腰三角形c一個(gè)外角的平分線平行于一邊的三角形是等腰三角形d兩個(gè)內(nèi)角不相等的三角形不是等腰三角形顯示解析3下列選項(xiàng)中，可以用來(lái)證明命題“若a21，則a1”是假命題的反例是（）aa=-2ba=-1ca=1da=2顯示解析4反證法證明“三角形中至少有一個(gè)角不小于60”先應(yīng)

2、假設(shè)這個(gè)三角形中（）a有一個(gè)內(nèi)角小于60b每個(gè)內(nèi)角都小于60c有一個(gè)內(nèi)角大于60d每個(gè)內(nèi)角都大于60顯示解析5如圖，在abc中，ab=ac，e是ab的中點(diǎn)，以點(diǎn)e為圓心，eb為半徑畫弧，交bc于點(diǎn)d，連接ed并延長(zhǎng)到點(diǎn)f，使df=de，連接fc，若b=70，則f的度數(shù)是（）a40b70c50d45顯示解析6如圖所示的正方形網(wǎng)格中，網(wǎng)格線的交點(diǎn)稱為格點(diǎn)已知a、b是兩格點(diǎn)，如果c也是圖中的格點(diǎn)，且使得abc為等腰三角形，則點(diǎn)c的個(gè)數(shù)是（）a6b7c8d9顯示解析7如圖，一艘海輪位于燈塔p的南偏東70方向的m處，它以每小時(shí)40海里的速度向正北方向航行，2小時(shí)后到達(dá)位于燈塔p的北偏東40的n處，則n處

3、與燈塔p的距離為（）a40海里b60海里c70海里d80海里顯示解析二、填空題（共3小題，每小題3分，滿分9分）8如圖所示，在abc中，ab=ac，點(diǎn)d、e在bc邊上，abd=dae=eac=36，則圖中共有等腰三角形的個(gè)數(shù)是顯示解析9如圖，在abc中，b與c的平分線交于點(diǎn)o，過(guò)點(diǎn)o作debc，分別交ab、ac于點(diǎn)d、e若ab=5，ac=4，則ade的周長(zhǎng)是顯示解析10如圖，ad是abc的邊bc上的高，由下列條件中的某一個(gè)就能推出abc是等腰三角形的是bad=acd；bad=cad；ab+bd=ac+cd；ab-bd=ac-cd顯示解析三、解答題（共3小題，滿分0分）11證明題：如圖所示，在a

4、bc中，ab=ac，apbapc，求證：pbpc顯示解析12如圖，在abc中，ab=ac，ad是高，am是abc外角cae的平分線（1）用尺規(guī)作圖方法，作adc的平分線dn；（保留作圖痕跡，不寫作法和證明）（2）設(shè)dn與am交于點(diǎn)f，判斷adf的形狀（只寫結(jié)果）顯示解析13已知aob及其內(nèi)部一點(diǎn)p，試討論以下問(wèn)題的解答：（1）如圖，若點(diǎn)p在aob的平分線上，我們可以過(guò)p點(diǎn)作直線垂直于角平分線，分別交oa、ob于點(diǎn)c、d，則可以得到ocd是以cd為底邊的等腰三角形；若點(diǎn)p不在aob的平分線上（如圖），你能過(guò)p點(diǎn)作直線，分別交oa、ob于點(diǎn)c、d，得到ocd是等腰三角形，且cd是底邊嗎？請(qǐng)你在圖中

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