问题 填空题
|
a
|=|
b
|=|
c
|=1,
a
+
b
+
c
=0,则
a
c
+
b
c
+
a
b
=______.
答案

a
+
b
+
c
=
0

(

a
+
b
+
c
)2=0

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

|

a
|=|
b
|=|
c
|=1

a
c
+
b
c
+
a
b
=-
3
2

故答案为:-

3
2

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