Geometry
# Dot Product of Vectors

In the figure above, the point \(H\) is the perpendicular foot from point \(A\) on \(\overrightarrow{OB}.\) If \(\lvert\overline{OA}\rvert=7,\lvert\overline{OB}\rvert=9,\) and \(\lvert\overline{OH}\rvert=5,\) what is \(\overrightarrow{OA}\cdot\overrightarrow{OB}?\)

**Note:** The figure is not drawn to scale.

If \(\vec{u}, \vec{v},\) and \(\vec{w}\) are vectors, then which of the following is not a valid operation?

\[ \begin{align*} \text{A. } & \hspace{.35cm} (\vec{u}\cdot\vec{v}) + |\vec{w}| \\ \text{B. } & \hspace{.35cm} \vec{u}\cdot\vec{v}\cdot\vec{w} \\ \text{C. } & \hspace{.35cm} \vec{u}\cdot(\vec{v} - \vec{w}) \end{align*}\]

Remember! Both inputs for a dot product must be vectors.

If the vectors \(\vec{v}=(\sqrt{3},4,\sqrt{2})\) and \(\vec{u}=(\sqrt{6},0,k)\) are perpendicular, what must be the value of \(k?\)

Hint: If two vectors are perpendicular, then their dot product is 0.

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