2012年浙江省高考理科试卷第15题的题目是这样的:在△ABC中,M是BC的中点,AM=3,BC=10,则AB→·AC→=__.此题从表面上看是一个比较简单的向量数量积的运算题,但其实它揭示了平面向量数量积运算的一个十分重要的性质,下面先来证明以下一个平面向量数量积的运算性质:如图1,在△ABC中,设O是BC边上的中点,则 2012 Zhejiang Science Entrance Examination Subject Question 15 questions like this: In △ ABC, M is the midpoint of BC, AM = 3, BC = 10, AB → AC → = __ This question from the surface Seeing is a relatively simple vector quantity product of the arithmetic problem, but in fact it reveals a very important property of the quantity vector of the plane vector. The following first proves the operation property of the following number product of a plane vector: As shown in Figure 1, In ABC, let O be the midpoint on the edge of BC