初中数学人教版七年级上册1.2.2 数轴背景图ppt课件

这是一份初中数学人教版七年级上册1.2.2 数轴背景图ppt课件，共25页。PPT课件主要包含了画数轴注意事项，解析如图，-10或6等内容，欢迎下载使用。

1.掌握数轴的概念，理解数轴上的点和有理数的对应关系.(重点）Master the cncept f number line and understand the crrespnding relatinship between pints n the number line and ratinal numbers.2.会正确的画出数轴，利用数轴上的点表示有理数.（难点）Be able t draw the number line crrectly and use the pints n the number line t represent ratinal numbers.
问题：在一条东西向的马路上，有一个汽车站牌，汽车站牌东3m和7.5m处有一棵柳树和一棵杨树，汽车站西3m和4.8m处分别有一棵槐树和一根电线杆，试画图表示这一情境．Questin: On a rad, there is a bus stp sign. There are a willw and a pplar at 3m and 7.5m in the east f the bus stp sign, and a lcust tree and a telegraph ple at 3m and 4.8m in the west f the bus stp. Try t draw a picture t shw the psitin.
怎样简明地表示这些树、电线杆与汽车站牌的相对位置关系（方向、距离）？Hw t cncisely express the relative psitin relatinship (directin and distance) between these trees, telegraph ples and bus stp signs?
-4.8 -3 0 1 3 7.5
为了使表达更清楚，我们规定向东为正，把点汽车站牌左右两边的数分别用负数和正数表示. In rder t make the expressin mre clear, we stipulate that the number n the left and right sides f the bus stp sign is psitive and negative respectively
我们把正数、0和负数用一条直线上的点表示出来.We express psitive, zer and negative numbers as pints n a straight line
观察如图所示的温度计，回答下列问题：Observe the thermmeter as shwn in the figure and answer the fllwing questins:（1）点A表示多少摄氏度？点B呢？点C呢？What degree des pint a mean? What abut pint B,C? （2）温度计刻度的正负是怎样规定的?以什么为基准?Hw is the psitive and negative f the thermmeter scale specified? Based n what?（3）每摄氏度两条刻度线之间的距离有什么特点?What are the characteristics f the distance between tw scale lines per centigrade?
活动：把温度计平放，我们能从中发现什么？Activity: Put the thermmeter flat. What can we find frm it?
思考：你能借鉴温度计,用一条直线上的点表示有理数吗? Can yu represent ratinal numbers by pints n a straight line?
画一条水平直线，在直线上取一点表示0，并把这个点叫作原点，选取某一长度作为单位长度，规定直线上向右的方向为正方向，就得到下面的数轴.Draw a hrizntal straight line, take a pint n the straight line t represent 0, call this pint the rigin, select a certain length as the unit length, and specify the right directin n the straight line as the psitive directin ,then we can get the fllwing number line.
1.画一条水平直线，定原点(如图)，原点表示0.Draw a hrizntal straight line and select a pint as the rigin , and the rigin represents 0.
2.规定从原点向右为正方向，那么相反的方向(从原点向左)则为负方向.If it is specified that the directin frm the rigin t the right is psitive, then the ppsite directin (frm the rigin t the left) is negative.
3.选择适当的长度为单位长度.Select the apprpriate length as the unit length.
原点、正方向、单位长度一个也不能少The rigin Psitive directin Unit length
判断下面所画数轴是否正确，并说明理由Judge whether the number line drawn belw is crrect and explain the reasns.
(1)原点、单位长度和正方向三要素缺一不可；Origin, unit length and psitive directin are indispensable;(2)直线一般画水平的；Straight lines are generally drawn hrizntally;(3)正方向用箭头表示，一般取从左到右；The psitive directin is indicated by an arrw, generally frm left t right.(4)取单位长度应结合实际需要，但要做到刻度均匀.The unit length shall be taken accrding t the actual needs, but the scale shall be unifrm.
-3 -2 -1 1 2 3
1.观察上面数轴，哪些数在原点的左边，哪些数在原点的右边，由此你有什么发现？Observe the number line abve, which numbers are n the left and right f the rigin. What d yu find?2.每个数到原点的距离是多少？由此你又有什么发现？What is the distance frm each number t the rigin? S what did yu find?
-3 -2 -1 1 2 3
注意:①把点标在线上；Mark the pint n the line;②把数标在点的上方，以便观看.Mark the number abve the pint.
任何一个有理数都可以用数轴上的一个点来表示.Any ratinal number can be represented by a pint n the number line.
一般地，设a是一个正数，则数轴上表示数a在原点的____边，与原点的距离是____个单位长度；表示数-a的点在原点的____边，与原点的距离是____个单位长度．Generally, let a be a psitive number, then psitive a t the right zer, and the distance frm the rigin is a unit length; negative number - a is t the left f zer, and the distance frm the rigin is a unit length.
1 2
-2 -1
例2 在下面数轴上，A，B，C，D各点分别表示什么数On the fllwing number line, what numbers d pints A, B, C and D represent respectively?
D C B A
(4) D点表示-1.5
(1)A 点表示2；
(2) B 点表示0.25；
(3)C点表示-0.75；
例3 从数轴上表示-1的点出发，向左移动两个单位长度到点B，则点B表示的数是 ，再向右移动5个单位长度到达点C，则点C表示的数是 .Example 3 Starting frm the pint representing - 1 n the number line, mve tw unit lengths t the left t pint B, then pint B represented the number ___, and then mve five unit lengths t the right t reach pint C, pint C represented the number ___.
点A为数轴上表示－2的动点，当点A沿数轴移动4个单位长度到点B时，点B所表示的数为 Pint A is the mving pint representing - 2 n the number line. When pint A mves 4 unit lengths alng the number line t pint B, the number represented by pint B is ( ) A.2 B.－6 C.2或－6 D.不同于以上
分析:点A可能向左移，也可能向右移，所以需分情况讨论.Pint a may mve left r right, s it needs t be discussed.
1.下列说法中正确的是 Which f the fllwing statements is crrect （ ）A. 在数轴上的点表示的数不是正数就是负数The number represented by a pint n the number line is either psitive r negative.B.数轴的长度是有限的The length f the number line is limited.C. 一个有理数总可以在数轴上找到一个表示它的点We can always find a pint representing a ratinal number n the number line.D. 所有整数都可以用数轴上的点表示，但分数就不一定能找到表示它的点All integers can be represented by pints n the number line, but fractins d nt necessarily.
2.与原点距离是2.5个单位长度的点所表示的有理数是The ratinal number represented by a pint with a distance f 2.5 units frm the rigin is （ ） A．2.5 B．-2.5 C．±2.5 D．这个数无法确定3．在数轴上到表示-2的点相距8个单位长度的点表示的数为________．On the number line, the number 8 units lng frm the pint representing - 2 is_______.
4.如图，写出数轴上点A，B，C，D，E表示的数． As shwn in the figure, write the numbers represented by pints A, B, C, D and E n the number line.
解：点A，B，C，D，E表示的数分别是The numbers represented by pints a, B, C, D and E are 0，-2，1，2.5，-3.
5. 画出数轴并表示下列有理数 Draw the number line and represent the fllwing ratinal numbers： 1.5，－2.2，－2.5， ， 　，0.
-3 -2 -1 0 1 2 3 4 5
1.数轴的定义：规定了原点、正方向和单位长度的直线叫数轴.Definitin f number line: a straight line that specifies the rigin, psitive directin and unit length is called number line.
2.数轴的画法.Drawing methd f number line.
3.所有的有理数都可以用数轴上的点来表示，原点右边的数是正数，原点左边的数是负数，0是正负数的分界限.All ratinal numbers can be represented by pints n the number line. The number n the right f the rigin is psitive, the number n the left f the rigin is negative, and 0 is the dividing pint f psitive and negative numbers.