![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/d01373f082025aafe440e466faedab64034f1a28?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
追问![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/a8ec8a13632762d0871a2a12a1ec08fa513dc673?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
这步,为什么可以展开,这个你必须说清楚。
追答矢量运算的分配率。
数量积的几何定义和坐标定义是等价的,证明的一方面:由几何定义导出坐标定义,这个很简单;
另一方面,由坐标定义导出几何定义,可如下证明(利用余弦定理)
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/342ac65c103853435ee60e8c9213b07eca808876?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
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追问你的证明过程是有点荒唐的,你自己仔细想想,余弦定理就是靠向量证明的,你直接用结论(余弦定理)来证明上面的,显得很荒唐。
追答你难道不知道余弦定理的几何证明(三角函数证明)方法吗。
去百度百科:余弦定理
追问你qq多少,请求援助,之后高分悬赏,以此回报,谢谢。
追答eight five two six one zero one eight three