设0＜θ＜，向量=（sin2θ，cosθ），=（1，﹣cosθ），若•=0，则tanθ=___

设0＜θ＜，向量=（sin2θ，cosθ），=（1，﹣cosθ），若•=0，则tanθ=______．

答案

　．

【考点】平面向量数量积的运算．

【分析】由条件利用两个向量的数量积公式求得 2sinθcosθ﹣cos²θ=0，再利用同角三角函数的基本关系求得tanθ

【解答】解：∵ =sin2θ﹣cos²θ=2sinθcosθ﹣cos²θ=0，0＜θ＜，

∴2sinθ﹣cosθ=0，∴tanθ=，

故答案为：．

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设0＜θ＜，向量=（sin2θ，cosθ），=（1，﹣cosθ），若•=0，则tanθ=___

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