$(a_1^2+a_2^2+\cdots+a_n^2)(b_1^2+b_2^2+\cdots+b_n^2)\ge(a_1b_1+a_2b_2+\cdots+a_nb_n)^2$
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$a_i,b_i\in\mathbb{R}$
$\left(\sum_{i=1}^{n}a_i^2\right)^{\frac12} \left(\sum_{i=1}^{n}b_i^2\right)^{\frac12} \ge \left| \sum_{i=1}^{n}a_ib_i \right|$
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[[벡터,vector]]로 나타내면
 $|\vec{x}| |\vec{y}| \ge |\vec{x} \cdot \vec{y}| $
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$|\vec{A}\cdot\vec{B}|^2\le(\vec{A}\cdot\vec{A})(\vec{B}\cdot\vec{B})$
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Up: [[부등식,inequality]]