Thread: Vectors
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Old June 27th, 2009, 04:05 PM
Plato Plato is offline
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Your notation is incorrect.
\begin{gathered} \overrightarrow {AB} = - 3i - j = \left\langle { - 3, - 1} \right\rangle \hfill \\ \left\| {\overrightarrow {AB} } \right\| = \left\| {\left\langle { - 3, - 1} \right\rangle } \right\| = \sqrt {\left( { - 3} \right)^3 + \left( { - 1} \right)^2 } \hfill \\ \end{gathered}

Then \overrightarrow {AC} = \left\langle {3, - 4} \right\rangle \; \Rightarrow \;m\left( {\angle BAC} \right) = \arccos \left( {\frac{{\overrightarrow {AB} \cdot \overrightarrow {AC} }} {{\left\| {\overrightarrow {AB} } \right\|\left\| {\overrightarrow {AC} } \right\|}}} \right)

Now you do the others.
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