问题
解答题
已知在△ABC中，|
|
答案
∵2
•AB
+|CA
|2=0，∴AB
•AB
=AC
|1 2
|2AB
∴cosA=
=
•AB AC |
||AB
|AC
=
|1 2
|2AB |
|2AB 1 2
∴A=60°
又∵|
|=|AB
|，AC
△ABC的形状为等边三角形．
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已知在△ABC中，|
|
∵2
•AB
+|CA
|2=0，∴AB
•AB
=AC
|1 2
|2AB
∴cosA=
=
•AB AC |
||AB
|AC
=
|1 2
|2AB |
|2AB 1 2
∴A=60°
又∵|
|=|AB
|，AC
△ABC的形状为等边三角形．