题目内容
已知
=(1,1),
=(4,1),
=(4,5),则
与
夹角的余弦值为( )
OA |
OB |
OC |
AB |
AC |
A.
| B.
| ||||
C.0 | D.以上结果都不对 |
∵
=
-
=(4,1)-(1,1)=(3,0),
=
-
=(4,5)-(1,1)=(3,4).
∴
•
=(3,0)•(3,4)=9
∴cos<
,
>=
=
=
.
故选:B.
AB |
OB |
OA |
AC |
OC |
OA |
∴
AB |
AC |
∴cos<
AB |
AC |
| ||||
|
|
9 | ||
3×
|
3 |
5 |
故选:B.
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