问题
选择题
若
|
答案
•e1
=|e2
||e1
|cos60°=e2 1 2
∴
•a
=(b
+2e1
)•(-3e2
+2e1
)e2
=-6
2+e1
•e1
+2e2 e 2
=-6+
+2=-1 2 7 2
故选D．
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若
|
•e1
=|e2
||e1
|cos60°=e2 1 2
∴
•a
=(b
+2e1
)•(-3e2
+2e1
)e2
=-6
2+e1
•e1
+2e2 e 2
=-6+
+2=-1 2 7 2
故选D．