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已知两向量op1=(cosθ,sinθ),op2=(1,-1),则向量p1p2模的最小值是?

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已知两向量op1=(cosθ,sinθ),op2=(1,-1),则向量p1p2模的最小值是?
P1P2 = OP2-OP1=(1-cosθ,-1-sinθ)
|OP2-OP1|^2
=(1-cosθ)^2+(-1-sinθ)^2
= 3 +2(sinθ-cosθ)
= 3+2√2sin(θ-π/4)
min P1P2 = √(3-2√2)
再问: 结果不能化简么?怎么化简啊
再答: let a - c√d = √(3-2√2) (a - c√d)^2 = (3-2√2) a^2+c^2d - 2ac√d = 3-2√2 => d = 2 2ac = 2 (1) a^2+2c^2 = 3 (2) solving (1) (2) a = -1, c =1 √(3-2√2) = √2-1