向量的数乘
2(2(3向量数乘运算及其几何意义
一选择题
111(化简的结果是 ( ) [(2a,8b),(4a,2b)]32
A( B( C( D( 2a,b2b,ab,aa,b2(已知,则下列命题正确的是 ( ) ,,R
A( B( C( D( ,,aa,,,aa,,,aa,,a,03(下列各式计算正确的有 ( )
(1)(,7)6a=-42a (2)7(a+b),8b=7a+15b
(3)a,2b+a+2b=2a (4)若a=m+n,b=4m+4n,则a?b
A(1个 B(2个 C(3 D(4个 4(已知E、F分别为四边形ABCD的边CD、BC边上的中点,设,,则= EFADa,BAb,
1111A( B( C( D( ( ) ,,()ab()ab,()ba,,,()ab2222
5(若化简 ( ) 3(2)2(3)2()abbcab,,,,,abc,,
A( B( C( D( 以上都不对 acb
6(已知四边形ABCD是菱形,点P在对角线AC上(不包括端点A、C),则= AP
( )
2A( B( ,,().(0,1)ABAD,,,,,,().(0,)ABBC2
2C( D( ,,().(0,1)ABAD,,,,,,().(0,)ABBC2二、填空题
7(已知、是实数,、是向量,对于命题: mnab
? ?mabmamb(),,,()mnamana,,,
?若,则 ?若,则 mana,mn,mamb,ab,
其中正确命题为_____________________(
8(计算:
(1)=__________; 3(53)2(6)abab,,,
(2)=__________( 4(35)2(368)abcabc,,,,,,
9(已知向量,,且,则=__________( 3()2(2)4()xaxaxab,,,,,,,0axb
10(若向量、满足,、为已知向量,则 y23,32xyaxyb,,,,xab
=__________; =___________( yx
三、解答题
111(如图,在ABC中,G是ABC的重心,证明: ,,AGABAC,,,,3
A
G
BCD