问题
选择题
已知平面上三点A、B、C满足|
|
答案
∵|
|=3，|AB
|=4，|BC
|=5CA
∴|
|2+|AB
|2=|BC
|2CA
∴∠B=90°
∴
•AB
+BC
•BC
+CA
•CA AB
=
(CA•
+BC
)AB
=
•CA AC
=-
2AC
=-25
故选B
搜题请搜索小程序“爱下问搜题”
已知平面上三点A、B、C满足|
|
∵|
|=3，|AB
|=4，|BC
|=5CA
∴|
|2+|AB
|2=|BC
|2CA
∴∠B=90°
∴
•AB
+BC
•BC
+CA
•CA AB
=
(CA•
+BC
)AB
=
•CA AC
=-
2AC
=-25
故选B