问题 选择题
△ABC中
AB
=
a
BC
=
b
CA
=
c
|
a
|=
2
,|
b
|=1,|
c
|=1
a
b
+
b
c
+
c
a
=(  )
A.0B.2C.-2D.-
2
答案

AB
+
BC
+
CA
=
0

a
+
b
+
c
=
0

a
+
b
+
c
)2=0

a
2
b
2
c
2
+2(
a
b
+
a
c
+
b
c
)=0

|

a
|=
2
,|
b
|=1,|
c
|=1

a
b
+
b
c
+
c
a
=-2

故选C

阅读理解
单项选择题