问题
选择题
△ABC中,AB边的高为CD,若
|
答案
∵
•a
=0,b
∴CA⊥CB
∵CD⊥AB
∵|
|=1,|a
|=2b
∴AB=5
由射影定理可得,AC2=AD•AB
∴AD=
=4 5 4 5 5
∴
=AD AB
=4 5 5 5 4 5
∴
=AD 4 5
=AB
(4 5
-CB
)=CA
(4 5
-a
)b
故选D
△ABC中,AB边的高为CD,若
|
∵
•a
=0,b
∴CA⊥CB
∵CD⊥AB
∵|
|=1,|a
|=2b
∴AB=5
由射影定理可得,AC2=AD•AB
∴AD=
=4 5 4 5 5
∴
=AD AB
=4 5 5 5 4 5
∴
=AD 4 5
=AB
(4 5
-CB
)=CA
(4 5
-a
)b
故选D