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9.2 坐标方法的简单应用
9.2.1 用坐标表示地理位置
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1.了解用平面直角坐标系来表示地理位置的意义及主要过程,能够用坐标系来描述地理位置.2.在实际问题中,能建立适当的平面直角坐标系,描述物体的位置.3.在平面上,运用方位角和距离刻画两个物体的相对位置.
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知识点一 用坐标表示地理位置
1.建立平面直角坐标系表示位置的步骤:
(1)建立平面直角坐标系,选择一个适当的参照点为原点,确定x轴、y轴的正方向.
(2)根据具体问题,确定单位长度.
(3)在坐标平面内画出这些点,写出各点的坐标和各个地点的名称.
练习1 小刚同学绘制了自己学校的平面示意图(如图),已知图书馆、行政楼的坐标分别为(-3,2),(2,3).
(1)请根据题意在图中建立平面直角坐标系;
(2)写出图中其他地点的坐标;
(3)在图中表示出体育馆(-1,-3)的位置;
(4)如果1个单位长度表示40 m,求实验楼到校门口的实际距离.
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【答案】(1)图略
(2)校门口(1,0),实验楼(-4,0),综合楼(-5,-3),信息楼(1,-2).
(3)图略
(4)200 m
知识点二 用方向角和距离表示地理位置
2.利用方向角和距离表示地理位置:以一点为参照点,用某个方向(方向角)加上与该参照点的距离来确定一个点的位置.
练习2 (教材P73例题变式)如图,4艘渔船在回港途中遭遇8级强风,小岛上的搜救队接到命令后立即准备搜救.假设你是指挥搜救队长,你能告诉搜救人员这些渔船的位置吗?
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【解】渔船A位于小岛的北偏东40°,25 n mile处;渔船B位于小岛的正南方向,20 n mile处;渔船C位于小岛的北偏西30°,30 n mile处;渔船D位于小岛的东偏南25°,35 n mile处.
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1.小明同学的座位位于第2列第5排,小丽同学的座位位于第4列第3排,若小明的座位用坐标表示为(2,5),则小丽的座位用坐标表示是( B ).
A.(3,4) B.(4,3)
C.(3,3) D.(4,4)
2.如图,小刚在小明的北偏东60°方向的500 m处,则小明在小刚的________方向的________m处.(请用方向和距离描述小明相对于小刚的位置)
【答案】南偏西60° 500
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3.如图,已知A村庄的坐标为(2,-3),晓彤骑自行车从原点O出发在x轴上行驶.行驶过程中当晓彤离A村庄最近时,晓彤所在的坐标为________.
【答案】(2,0)
4.如图,在一个平面区域内,一台雷达探测器测得在点A,B,C处有目标出现.按某种规则,点A,B的位置可以分别表示为(1,90°),(2,240°),则点C的位置可以表示为____________.
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【答案】(3,30°)
5.如图,一艘船在A处遇险后向相距25 km位于B处的救生船求救,可将救生船B相对于遇险船A的位置表示为(北偏东60°,25).
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(1)货船C与遇险船A相距15 km,且AC⊥AB,那么货船C相对于遇险船A的位置应怎样表示?
(2)如果小岛D相对于遇险船A的位置为(南偏东50°,20),请在图中画出小岛D.
【解】(1)货船C与遇险船A相距15 km,且AC⊥AB,
所以货船C相对于遇险船A的位置表示为(北偏西30°,15).
(2)图略
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6.下图是某寄宿制学校的平面示意图,已知旗杆的位置是(-2,3),实验室的位置是(1,4).
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(1)请你画出该学校平面示意图所在的坐标系;
(2)办公楼的位置是(-2,1),教学楼的位置是(2,2),在图中标出办公楼和教学楼的位置;
(3)写出食堂、图书馆的坐标.
【答案】(1)图略 (2)图略
(3)食堂(-5,5)、图书馆(2,5).
7.为了更好地开展景区规划工作,某景区对景区内的5个景观利用坐标确定了位置,并且设置了导航路线.
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(1)在如图所示的正方形网格中建立平面直角坐标系xOy,使得景观A,B的位置分别表示A(1,2),B(0,-1);
(2)在建立的坐标系中,景观C的坐标为________;
(3)在坐标系中标出D(-3,-2),E(2,-2)的位置,连接AC,DE,直接写出AC与DE的位置关系.
【答案】(1)图略
(2)(-1,2) (3)图略 AC∥DE
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8.如图,学校对应点A的坐标为(2,a),图书馆对应点B的坐标为(b,-2).(图中小正方形的边长代表1个单位长度),解答以下问题:
(1)请补全原有的平面直角坐标系,a=________,b=________;
(2)若体育馆对应点C的坐标为(3,-1),画出三角形ABC,求三角形ABC的面积.
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【解】(1)图略 1 -1
(2)图略,三角形ABC的面积为4×3-×4×1-×2×1-×3×3=4.5.9.2.2 用坐标表示平移
1.在平面直角坐标系中,能写出一个已知顶点坐标的多边形沿坐标轴方向平移一定距离后图形的顶点坐标,知道对应顶点坐标之间的关系.2.在平面直角坐标系中,探索并了解将一个多边形依次沿两个坐标轴方向平移后所得到的图形和原来图形具有平移关系,体会图形顶点坐标的变化.3.会根据图形上点的坐标的变化,来判定图形的平移过程.
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知识点一 坐标系中点的平移
1.(1)左右平移:点在平面直角坐标系中进行左右平移时,纵坐标 ,横坐标进行 .向右平移时 ,向左平移时 .
巧记:左右平移,横加减,纵不变,右加左减.
(2)上下平移:点在平面直角坐标系中进行上下平移时,横坐标 ,纵坐标进行 .向上平移时 ,向下平移时 .
巧记:上下平移,纵加减,横不变,上加下减.
练习1 在平面直角坐标系中,已知点A的坐标为(1,4),如果将点A向右平移2个单位长度得到点A′,则点A′的坐标为( ).
A.(1,6) B.(1,2)
C.(3,4) D.(-1,4)
知识点二 坐标系中图形的平移
2.图形平移时,把图形的关键点按照点的平移进行平移,然后把平移后的点按照 连接.因为图形是整体平移,所以图形上的每一个点都遵循同一个平移规律.
练习2 三角形ABC所在平面内任意一点P(a,b)经过平移后对应点为P1(c,d),已知A(2,3)经过此次平移后对应点为A1(5,-1),则a+b-c-d的值为( ).
A.1 B.-1
C.5 D.-5
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基础巩固
1.在平面直角坐标系中,把点P(-1,-2)先沿x轴向左平移3个单位长度,再沿y轴向下平移3个单位长度得到对应点P′,则点P′的坐标是( ).
A.(2,1) B.(2,-5)
C.(-4,-5) D.(-4,1)
2.在平面直角坐标系中,将点A(m,n+2)先向左平移3个单位长度,再向上平移2个单位长度,得到点A′.若点A′的坐标为(2,3),则m+n的值是( ).
A.6 B.4
C.-4 D.-6
3.将点P(m+2,2m+4)向右平移1个单位长度到点P′,若点P′在y轴上,那么点P′的坐标是________.
4.在平面直角坐标系中,线段A′B′是由线段AB经过平移得到的,已知点A(-3,2)的对应点为A′(2,-1),点B的对应点B′的坐标为(6,1),则点B的坐标为________.
5.在平面直角坐标系中,已知A(-2,0),将点A向下平移1个单位长度,再向右平移2个单位长度得到点B,若点C在y轴上,且三角形ABC的面积等于3,则点C的坐标为____________.
6.已知线段AB的中点为P(a,b),若A(1,1)经过平移到达A′(4,8),则点P经过平移后的对应点P′的坐标为________.
7.如图,已知三角形ABC在平面直角坐标系中.
(1)写出三角形ABC各点的坐标:A________,B________,C________;
(2)若三角形ABC向下平移2个单位长度,再向左平移2个单位长度得到三角形A′B′C′,在平面直角坐标系中画出三角形A′B′C′,并写出点A′,B′,C′的坐标;
(3)求出三角形A′B′C′的面积.
8.(跨学科融合)下图是一组密码的一部分,为了保密,不同的情况下可以采用不同的密码.若输入数字密码(7,7),(8,5),对应中转口令是“数学”,最后输出口令为“文化”.按此方法,若输入数字密码(2,7), (3,4),则最后输出口令为( ).
A.相交 B.平行
C.素养 D.垂直9.2.2 用坐标表示平移
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1.在平面直角坐标系中,能写出一个已知顶点坐标的多边形沿坐标轴方向平移一定距离后图形的顶点坐标,知道对应顶点坐标之间的关系.2.在平面直角坐标系中,探索并了解将一个多边形依次沿两个坐标轴方向平移后所得到的图形和原来图形具有平移关系,体会图形顶点坐标的变化.3.会根据图形上点的坐标的变化,来判定图形的平移过程.
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知识点一 坐标系中点的平移
1.(1)左右平移:点在平面直角坐标系中进行左右平移时,纵坐标不变,横坐标进行加减.向右平移时加,向左平移时减.
巧记:左右平移,横加减,纵不变,右加左减.
(2)上下平移:点在平面直角坐标系中进行上下平移时,横坐标不变,纵坐标进行加减.向上平移时加,向下平移时减.
巧记:上下平移,纵加减,横不变,上加下减.
练习1 在平面直角坐标系中,已知点A的坐标为(1,4),如果将点A向右平移2个单位长度得到点A′,则点A′的坐标为( C ).
A.(1,6) B.(1,2)
C.(3,4) D.(-1,4)
知识点二 坐标系中图形的平移
2.图形平移时,把图形的关键点按照点的平移进行平移,然后把平移后的点按照原图形连接.因为图形是整体平移,所以图形上的每一个点都遵循同一个平移规律.
练习2 三角形ABC所在平面内任意一点P(a,b)经过平移后对应点为P1(c,d),已知A(2,3)经过此次平移后对应点为A1(5,-1),则a+b-c-d的值为( A ).
A.1 B.-1
C.5 D.-5
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1.在平面直角坐标系中,把点P(-1,-2)先沿x轴向左平移3个单位长度,再沿y轴向下平移3个单位长度得到对应点P′,则点P′的坐标是( C ).
A.(2,1) B.(2,-5)
C.(-4,-5) D.(-4,1)
2.在平面直角坐标系中,将点A(m,n+2)先向左平移3个单位长度,再向上平移2个单位长度,得到点A′.若点A′的坐标为(2,3),则m+n的值是( B ).
A.6 B.4
C.-4 D.-6
3.将点P(m+2,2m+4)向右平移1个单位长度到点P′,若点P′在y轴上,那么点P′的坐标是________.
【答案】(0,-2)
4.在平面直角坐标系中,线段A′B′是由线段AB经过平移得到的,已知点A(-3,2)的对应点为A′(2,-1),点B的对应点B′的坐标为(6,1),则点B的坐标为________.
【答案】(1,4)
5.在平面直角坐标系中,已知A(-2,0),将点A向下平移1个单位长度,再向右平移2个单位长度得到点B,若点C在y轴上,且三角形ABC的面积等于3,则点C的坐标为____________.
【答案】(0,2)或(0,-4)
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6.已知线段AB的中点为P(a,b),若A(1,1)经过平移到达A′(4,8),则点P经过平移后的对应点P′的坐标为________.
【答案】(a+3,b+7)
7.如图,已知三角形ABC在平面直角坐标系中.
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(1)写出三角形ABC各点的坐标:A________,B________,C________;
(2)若三角形ABC向下平移2个单位长度,再向左平移2个单位长度得到三角形A′B′C′,在平面直角坐标系中画出三角形A′B′C′,并写出点A′,B′,C′的坐标;
(3)求出三角形A′B′C′的面积.
【答案】(1)(2,3) (1,0) (3,0)
(2)图略.
A′(0,1),B′(-1,-2),C′(1,-2).
(3)3
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8.(跨学科融合)下图是一组密码的一部分,为了保密,不同的情况下可以采用不同的密码.若输入数字密码(7,7),(8,5),对应中转口令是“数学”,最后输出口令为“文化”.按此方法,若输入数字密码(2,7), (3,4),则最后输出口令为( A ).
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A.相交 B.平行
C.素养 D.垂直9.2 坐标方法的简单应用
9.2.1 用坐标表示地理位置
1.了解用平面直角坐标系来表示地理位置的意义及主要过程,能够用坐标系来描述地理位置.2.在实际问题中,能建立适当的平面直角坐标系,描述物体的位置.3.在平面上,运用方位角和距离刻画两个物体的相对位置.
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知识点一 用坐标表示地理位置
1.建立平面直角坐标系表示位置的步骤:
(1)建立平面直角坐标系,选择一个适当的参照点为 ,确定x轴、y轴的 .
(2)根据具体问题,确定 .
(3)在坐标平面内画出这些点,写出各点的坐标和各个地点的名称.
练习1 小刚同学绘制了自己学校的平面示意图(如图),已知图书馆、行政楼的坐标分别为(-3,2),(2,3).
(1)请根据题意在图中建立平面直角坐标系;
(2)写出图中其他地点的坐标;
(3)在图中表示出体育馆(-1,-3)的位置;
(4)如果1个单位长度表示40 m,求实验楼到校门口的实际距离.
2.利用方向角和距离表示地理位置:以一点为参照点,用某个方向( )加上与该参照点的 来确定一个点的位置.
练习2 (教材P73例题变式)如图,4艘渔船在回港途中遭遇8级强风,小岛上的搜救队接到命令后立即准备搜救.假设你是指挥搜救队长,你能告诉搜救人员这些渔船的位置吗?
1.小明同学的座位位于第2列第5排,小丽同学的座位位于第4列第3排,若小明的座位用坐标表示为(2,5),则小丽的座位用坐标表示是( ).
A.(3,4) B.(4,3)
C.(3,3) D.(4,4)
2.如图,小刚在小明的北偏东60°方向的500 m处,则小明在小刚的________方向的________m处.(请用方向和距离描述小明相对于小刚的位置)
3.如图,已知A村庄的坐标为(2,-3),晓彤骑自行车从原点O出发在x轴上行驶.行驶过程中当晓彤离A村庄最近时,晓彤所在的坐标为________.
4.如图,在一个平面区域内,一台雷达探测器测得在点A,B,C处有目标出现.按某种规则,点A,B的位置可以分别表示为(1,90°),(2,240°),则点C的位置可以表示为____________.
5.如图,一艘船在A处遇险后向相距25 km位于B处的救生船求救,可将救生船B相对于遇险船A的位置表示为(北偏东60°,25).
(1)货船C与遇险船A相距15 km,且AC⊥AB,那么货船C相对于遇险船A的位置应怎样表示?
(2)如果小岛D相对于遇险船A的位置为(南偏东50°,20),请在图中画出小岛D.
6.下图是某寄宿制学校的平面示意图,已知旗杆的位置是(-2,3),实验室的位置是(1,4).
(1)请你画出该学校平面示意图所在的坐标系;
(2)办公楼的位置是(-2,1),教学楼的位置是(2,2),在图中标出办公楼和教学楼的位置;
(3)写出食堂、图书馆的坐标.
7.为了更好地开展景区规划工作,某景区对景区内的5个景观利用坐标确定了位置,并且设置了导航路线.
(1)在如图所示的正方形网格中建立平面直角坐标系xOy,使得景观A,B的位置分别表示A(1,2),B(0,-1);
(2)在建立的坐标系中,景观C的坐标为________;
(3)在坐标系中标出D(-3,-2),E(2,-2)的位置,连接AC,DE,直接写出AC与DE的位置关系.
8.如图,学校对应点A的坐标为(2,a),图书馆对应点B的坐标为(b,-2).(图中小正方形的边长代表1个单位长度),解答以下问题:
(1)请补全原有的平面直角坐标系,a=________,b=________;
(2)若体育馆对应点C的坐标为(3,-1),画出三角形ABC,求三角形ABC的面积.