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设a,b是两个平面向量,则等式a·b=1/4[(a+b)~2-(a-b)~2]恒成立.上面的等式的几何意义:向量的数量积可以表示为以这组向量为邻边的平行四边形的“和对角线”与“差对角线”平方差的1/4,即
Let a and b be two plane vectors, then the equation a · b = 1/4 [(a + b) ~ 2- (ab) ~ 2] holds. The geometric meaning of the above equation: It can be expressed as 1/4 of the square deviation of the “” and “diagonal ” and "