已知向量
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,
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的夾角為60°,|
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|=|
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|=2,若
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=2
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-
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,則△ABC為( )
A.等腰三角形 | B.等邊三角形 |
C.直角三角形 | D.等腰直角三角形 |
解:因為向量
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,
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的夾角為60°,|
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|=|
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|=2,若
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=2
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+
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所以,
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則利用三邊關(guān)系可知,該三角形為直角三角形。 選C
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在△
ABC中,角
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,
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,
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.則
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的面積為
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B.
C.
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已知
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是
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的圖象上任意兩點,設(shè)點

,且

,若
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,其中

,且
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.
(1)求
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的值;
(2)求
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;
(3)數(shù)列
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中
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,當(dāng)
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時,
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的前
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項和為
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,求
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的取值范圍使
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對一切

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已知向量
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,
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,其中
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,
求:(1)
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和
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的值;
(2)
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與
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夾角
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,
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,且
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.
(1)求
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及
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;
(2)若
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的最小值是
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,求實數(shù)
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已知平面向量
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滿足
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,且
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與
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的夾角為120°,
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,則
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的取值范圍是
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