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What is the dot product of two planar vectors $\vec{u} = (x_1, y_1)$ and $\vec{v} = (x_2, y_2)$, and what does $\vec{u} \cdot \vec{v} = 0$ imply for non-zero vectors?

Study flashcard from the deck Gaokao essentials: original practice.

Answer

$\vec{u} \cdot \vec{v} = x_1 x_2 + y_1 y_2 = |\vec{u}||\vec{v}|\cos\theta$; $\vec{u} \cdot \vec{v} = 0$ indicates that the vectors are orthogonal (perpendicular).

Explanation

Because $\cos(90^\circ) = 0$, non-zero vectors with a zero dot product meet at a right angle.

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