(完整word版)必修四平面向量的数量积讲义.pdf
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1、1 2.3 平面向量的数量积一、平面向量数量积1、定义:已知两个非零向量a与b,它们的夹角为,则数量ab cos叫做a与b的数量积(或内积),记作ab,即abab cos。注意:(1)两向量的数量积,其结果是个数量,而不是向量,它的值为两向量的模与两向量夹角的余弦的乘积,其符号由夹角的余弦值决定;(2)两个向量的数量积是两个向量之间的一种乘法,与以前学过的数的乘法不同,“”不能省略,也不能也成“”;(3)在运用数量积公式时,一定要注意两个向量夹角的范围:00180 0。(4)规定:零向量与任一向量的数量积为0,即0b0;(5)当向量a与b的夹角为900时,叫a与b互相垂直,记作:ab,此时:a
2、bab0。2、平面向量数量积的几何意义:(1)对于abab cos,其中b cos叫做b在a方向上的投影,当为锐角时,投影为正;当为钝角时,投影为负;当就直角时,投影为0;当为 0 度时,投影是b;当为 180 度时,投影为b;(2)a在b方向上的投影与b在a方向上的投影就不同的;(3)a在b方向上的投影值可以写成bba。例 1:已知a 2,b 5,当(1)a与b夹角为 300时;(2)当ab时;(3)当当ab时;分别计算a与b的数量积。【解析】:(1)53;(2)0;(3)10 变式练习 1:已知a 3,b 5,且a与b的夹角为450,则a在b方向上的投影是()A:223B:3 C:4 D:
3、5【解析】:A 2 变式练习 2:已知a 6,b 3,且ab 12,则a在b方向上的投影是()A:4 B:2 C:4 D:2【解析】:A 二、平面向量数量积的性质若a与b是非零向量,e是与a方向相同的单位向量,是e与a的夹角1、eaaeae cos2、abab0 3、若a与b同向,则abab(夹角为 0 度);若反向,则abab(夹角为 180度);特别地,aa(a)2a2或aaa4、若是a与b的夹角,则 cos baba5、abab(当a与b共线时取等号)三、平面向量数量积的运算律1、abba2、(a)b(ab)a(b)3、(ab)cacbc4、(ab)(ab)(a)2(b)2a2b25、(
4、ab)2a2 2abb2 注意:(1)没有(ab)ca(bc)这个运算定律;(2)acbc,则不能得到ab;(3)若ab0,则a0或b0或900。例 2:下列说法正确的个数_。(1)两个向量的数量积是一个向量;(2)向量在另一个向量方向上的投影也是向量;(3)若ab 0,则a与b的夹角为锐角,若ab0,则a与b的夹角为钝角;(4)(ab)ca(bc);(5)若ab0,则a0或b0。【解析】:0 个文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2
5、 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I1
6、0V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10
7、C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8
8、U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1
9、U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码
10、:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8
11、W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U93 例 3:已知a与b的夹角为1200,且a 4,b 2,则计算(a2b)(ab)_,ab _。【解析】:12 23例 4:已知OAAB,OA 4,则OAOB_。【解析】:16 变式练习 1:已知a 1,ab21,(ab)(ab)21,求(1)a与b的夹角;(2)ab与ab的夹角的余弦值。【解析】:450,ab221,ab225,cos25212155。变式练习 2
12、:已知向量a、b的夹角为 600,且a 2,b 1,则向量a与向量a2b的夹角等于()A:1500B:900C:600D:300【解析】:cosbaabaa2)2(300 可用数形结合法,构成的四边形为菱形变式练习 3:已知向量a与向量b满足,a 6,b 4,且a与b的夹角为600,求ab与a 3b。【解析】:ab 219,a3b 63变式练习 4:设四边形ABCD 为平行四边形,AB 6,AD 4,若点 M,N 满足BM3MC,DN2NC,则AMNM()A:20 B:15 C:9 D:6 解析】这个地方四边形ABCD 为平行四边形,可赋予此四边形为矩形,进而以A 为坐标原点建立坐标系。由0,
13、06,34,4A(),M()N(),进而(6,3)AM,(2,1)NM,9AMNM。文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:C
14、M7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9
15、R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 H
16、P9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V
17、9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6
18、 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5
19、Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U94 变式练习 5:已知向量a与向量b是两个互相垂直的单位向量,若向量c满足(ac)(
20、bc)0,则c的最大值是()A:1 B:2 C:2D:22【解析】:(ac)(bc)abacbcc20,则c2c(ab),则c4c(ab)2c2(a22abb2)2c2故c22。C 四、平面向量数量积的坐标表示、模、夹角设i,j为 x 轴、y 轴方向的两个单位向量,即i(1,0),j(0,1),且a与b为两个非零向量,a(x1,y1),b(x2,y2)1、ii1 jj1 ij0 abx1 x2y1y22、若a(x,y),则a222yx或a22yx。若 A(x1,y1),B(x2,y2),则AB212212)()(yyxx3、若a(x1,y1),b(x2,y2),则abab0 x1x2y1y20
21、 文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:
22、CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W
23、9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2
24、HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10
25、V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C6 ZS8U5Z5E1U9文档编码:CM7C8W9R2E2 HP9I10V9U10C
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