问题 填空题
已知|
a
|=|
b
|=|
a
-
b
|=2
,则|3
a
-2
b
|
=______.
答案

|

a
-
b
|=2

|

a
-
b
| 2=
a
 2-2
a
b
+
b
 2=4

|

a
|=|
b
|=2

∴4-2

a
• 
b
+4=4,可得
a
b
=2

因此,可得|3

a
-2
b
| 2=9
a
 2
-12
a
b
+4
b
 2
=36-24+16=28

|3

a
-2
b
|=
|3
a
-2
b
| 2
=
28
=2
7

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