设a，b，c均为向量，下列等式正确的是：
(A) (a + b)(a-b) = a 2 - b 2 (B) a.(a.b) = a 2 b
(C) (a.b)2 = a 2 b 2 (D) (a + b) × (a - b) = a × a - b × b
2023-06-01
参考答案：A
(a + b)(a -b) = a.a -a.b + b.a -b.b = a 2 - b 2，选项（A)正确； a.b = a b cosθ， (a.b)2 = a 2 b 2 cos2 θ，选项（C）错误；(a + b) x (a - b) = a x a - a x b + b x a - b x b = a x a - 2a x b - b x b，选项（D)错误。 点评：a.b = b.a a x b = -b x a
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