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已知向量,的夹角为,且,||=2,在△ABC中,,D为BC边的中点,则=A.2B.4C.6...
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已知向量
![](data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAA4AAAAWCAYAAADwza0nAAAAAXNSR0IArs4c6QAAAARnQU1BAACx
jwv8YQUAAAAgY0hSTQAAeiYAAICEAAD6AAAAgOgAAHUwAADqYAAAOpgAABdwnLpRPAAAAMJJREFU
OE/lU9sNgzAM9EjswxYeIkt4hw7gOSJlhyxxtR2CeAQpar+qRkICci8fgTC1CtKaUA5YmuI5qCQs
62uHky3MXwvSZvu541zUb2a8OMxH/UtiVXAcAkFGhXK/tzayxOGQfP9orVUn224WhtYMcREnxTsC
a70xg1iVjShQV3YCCyQeWoJHR1clVoM1ESJ33pLECMOoW7SW+eQQIiM7Q1JE65tRVHfoIjbnqByP
uYseRSyg7G0/tTr3i5xQP3TI311SXOM8e6ciAAAAAElFTkSuQmCC
)
,
![](data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAwAAAAWCAYAAAD0OH0aAAAAAXNSR0IArs4c6QAAAARnQU1BAACx
jwv8YQUAAAAgY0hSTQAAeiYAAICEAAD6AAAAgOgAAHUwAADqYAAAOpgAABdwnLpRPAAAAKlJREFU
OE/dU+0NhCAMZST3cYsOwRLs4ACdg4QdWOLZUjz1FNHE+3NNTCC+rxZwuKwEP3qkDcZdE+Rv8hjG
6QNzUuh/A3y1ee7wfg9fiv1I/0mICPXwQtQOM5jsMG2/rzolJQXEAiZwFhoTSBenhMwgYnAw8OLS
dFC1XYQqcNQHJJJl3qq14qi3k7Alzqq29BHBZz0c1FSgTE2H0JxS9xmtD+g+1JC/v60zWobH+S+C
TdAAAAAASUVORK5CYII=
)
的夹角为
![](data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAkAAAAjCAYAAABGpiBAAAAAAXNSR0IArs4c6QAAAARnQU1BAACx
jwv8YQUAAAAgY0hSTQAAeiYAAICEAAD6AAAAgOgAAHUwAADqYAAAOpgAABdwnLpRPAAAANJJREFU
OE/FU9sNxDAI41bOOmzCHEyRJSivRGnKXf56SJWi1MImNh/RglMZ6FRwAjjT6yAWBLAJH1+j7mqA
EYX10AnF7zpJayTxO2oKZ2wBYhSoQV2oRUcHoZ+2TkYBg7ZVIOuiopOik4LyzESpybuAjElceE46
WN9/8bPFFrfSknH/n6gswudDptl7CtwOuP+8R8WcT4OrB1FbwmDU8I2xt6Ro6LILcmSoooU1GkEV
mV+7FaCgn9HxjD9Ep8YlwVP4zPX3RVh3LxeiWqlfgXk5vhcoRz5Wn9bxVgAAAABJRU5ErkJggg==
)
,且
![](data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAADMAAAAWCAYAAABtwKSvAAAAAXNSR0IArs4c6QAAAARnQU1BAACx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)
,|
![](data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAwAAAAWCAYAAAD0OH0aAAAAAXNSR0IArs4c6QAAAARnQU1BAACx
jwv8YQUAAAAgY0hSTQAAeiYAAICEAAD6AAAAgOgAAHUwAADqYAAAOpgAABdwnLpRPAAAAKlJREFU
OE/dU+0NhCAMZST3cYsOwRLs4ACdg4QdWOLZUjz1FNHE+3NNTCC+rxZwuKwEP3qkDcZdE+Rv8hjG
6QNzUuh/A3y1ee7wfg9fiv1I/0mICPXwQtQOM5jsMG2/rzolJQXEAiZwFhoTSBenhMwgYnAw8OLS
dFC1XYQqcNQHJJJl3qq14qi3k7Alzqq29BHBZz0c1FSgTE2H0JxS9xmtD+g+1JC/v60zWobH+S+C
TdAAAAAASUVORK5CYII=
)
|=2,在△ABC中,
![](data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAMUAAAAWCAYAAABwklhxAAAAAXNSR0IArs4c6QAAAARnQU1BAACx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==
)
,D为BC边的中点,则
![](data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAB4AAAAWCAYAAADXYyzPAAAAAXNSR0IArs4c6QAAAARnQU1BAACx
jwv8YQUAAAAgY0hSTQAAeiYAAICEAAD6AAAAgOgAAHUwAADqYAAAOpgAABdwnLpRPAAAASBJREFU
SEvtlesNwyAMhD1S9skWDMES7NABPAdSdmAJ1zghD7DT9IH6o41UqYoin+87G4C6PRP50dNk1Idu
urnw5GkYb6rEQRgA6PO/gbxi+5uOI4UQOxDXMt602HEvYc3LX/hhxpEQ04FdDMYGnNZ6CnUidECu
Es5diLhD2lriwnklD+/2/T4hnNDJbrdGjIYSkuPvtUb3g3w+1VwkIGNmx42wCDhqQcwNgYr8kmP+
SJBlfK2AkFCRvikcQ2BJfsTZ8n+Ny85dcL6KuuS6nduVsIlZJo5nQotAxnE9JduMJdfd6uRCNVLt
ndBYptpcKUs4O6lE2ix1zIWSPs0lI0N4RlswLUOyXpWMWzAaB4e5u+Yed7iYLpTsex+fNPB7wndp
2kgXmJ8E8wAAAABJRU5ErkJggg==
)
=( )
A.2
B.4
C.6
D.8
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B.![](data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABYAAAASCAYAAABfJS4tAAAAAXNSR0IArs4c6QAAAARnQU1BAACx
jwv8YQUAAAAJcEhZcwAADsMAAA7DAcdvqGQAAAD8SURBVDhPzVQxEoQgDMy7KHiOPT+h5iG0eYgF
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C.![](data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAB8AAAASCAYAAACjMAXnAAAAAXNSR0IArs4c6QAAAARnQU1BAACx
jwv8YQUAAAAJcEhZcwAADsMAAA7DAcdvqGQAAAEJSURBVEhL1ZRNDoQgDIV7LhYcxz03Yc1B2HIQ
Fxylw6+UwSozjjFjYmKw6cd7fQB4wwMAOPXewE7gmWeuaqYTqfkvuDeyzUka9B+qpeWDcm9Q1hwo
t5UW2x2qi0AeTnuH77CJys9wp7aFC4KbIho47zsXnergHo2sR0NhM+X7bbCBCyJhtD2D4q4AJBoy
8LzGvKTR4cy33qEPB48NUvCYprNesMpL8GRRt3POr4fv6JwncSXc+/BPlNuljGXZD9y7XWTuA9yp
fuZnVltrU4kWgEKv6ZtXnsPdjhq9AMgZPIMO/5MDWX0Hj0pJYKmpP73blwCJ6h+521ctEIR+Bh4t
j+ofUV5zMAt/AYkk0Z8xTRTAAAAAAElFTkSuQmCC
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,且
,
,在△ABC中,
,D为BC边的中点,则
=( )
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